Erratics and Drift
In the nineteenth century, scientists theorized that glaciers (ice sheets) covered much of Earth’s surface during an ancient very cold period known as the ice age. Following efforts to map ancient glaciers, researchers concluded that there had been multiple ice advances and retreats. Evidence for multiple glaciations was tied to two types of glacial deposits: one called erratic boulders, often referred to simply as erratics, and a second, glacial drift-a general term for the loose, rocky debris distributed across the countryside by slowly moving glaciers. Erratic boulders are spread over large regions in Europe and North America; the most remarkable ones are very large and they are often quite different in makeup from the local bedrock. How they got there was unknown before scientists understood how ancient glaciers transported rocks. In the northeastern United States, where there are outcrops of very distinctive rock varieties, trails of erratics of a specific type can often be traced for hundreds of kilometers, fanning out over the countryside near their sources. Careful mapping of these erratic trails can provide an accurate picture of how the glaciers that carried the boulders moved across the land.
Before the ice age theory was generally accepted, most geologists and naturalists argued that the erratics had been transported by water to their current resting places. They realized that even fairly small boulders would sink instantly in normal streams, but they also understood enough about rare natural phenomena such as tidal waves and great storms to know that water could transport heavy objects under extreme conditions. But even extreme events could not easily explain the massive granite erratics in the European Jura Mountains, especially the ones that were perched high on valley walls, far above the streams below. Compounding the problem of interpreting these deposits, however, was the fact that at a few localities in Britain, where much of the most detailed research into the ice age controversy was being conducted, the fine-grained drift that accompanied the erratic boulders contained seashells. Critics of the hypothesis that glaciers had transported erratic boulders seized on this; they claimed it was conclusive evidence that the ocean was involved. They argued that the erratics must have been transported by great, violent floods coursing over the land, and they said that there were simply no modern-day counterparts. They knew that the sea had covered parts of the continents in the past, because fossilized fish were found throughout Europe. The marine shells in “glacial” drift, they asserted, were proof that the sea had invaded the land yet again and left the drift behind when it receded. It was not until much later that the true origin of the seashells in drift was realized. James Croll, a Scottish scientist, deduced that they too had been transported by glaciers, scraped up by the ice along with sediments from the shallow seas around Britain and carried inland. However, before their origin was understood, the shells were a serious difficulty for those who argued that drift and erratics were ice age deposits.
Still, notwithstanding the seashell argument, even some of the opponents of the glacial theory had to admit that it would be impossible to transport large erratic boulders in water over long distances, no matter how violent the storm or flood. So they came up with an ingenious solution: the erratics might indeed have been carried by ice, but ice that was floating on formerly more extensive seas, transporting boulders from a northerly source. If parts of the continents had been submerged in the past, they reasoned, the icebergs could have floated over the sunken land, dropping their rocky burden as they melted. That would explain the presence of ocean shells in the drift. It was the idea of drifting icebergs that first led to use of the term “drift” for the characteristically chaotic sediments left behind by glaciers-sediments that have neither the well-defined layers nor the uniformity of grain sizes that characterize those deposited in water. The term is still in use today, although the theory that drifting icebergs deposited the seashells, erratics, and other material has been abandoned.
1
In the nineteenth century, scientists theorized that glaciers (ice sheets) covered much of Earth’s surface during an ancient very cold period known as the ice age. Following efforts to map ancient glaciers, researchers concluded that there had been multiple ice advances and retreats. Evidence for multiple glaciations was tied to two types of glacial deposits: one called erratic boulders, often referred to simply as erratics, and a second, glacial drift-a general term for the loose, rocky debris distributed across the countryside by slowly moving glaciers. Erratic boulders are spread over large regions in Europe and North America; the most remarkable ones are very large and they are often quite different in makeup from the local bedrock. How they got there was unknown before scientists understood how ancient glaciers transported rocks. In the northeastern United States, where there are outcrops of very distinctive rock varieties, trails of erratics of a specific type can often be traced for hundreds of kilometers, fanning out over the countryside near their sources. Careful mapping of these erratic trails can provide an accurate picture of how the glaciers that carried the boulders moved across the land.
According to paragraph 1， all of the following are true of erratics EXCEPT:
Negative Factual Information Questions否定事实信息题
AThey leave longer trails in the northeastern United States than in other places.
BThey are found in wide areas of Europe and North America.
CThey can form trails hundreds of kilometers long.
DThey provide reliable evidence about past glacier movements.
2
Before the ice age theory was generally accepted, most geologists and naturalists argued that the erratics had been transported by water to their current resting places. They realized that even fairly small boulders would sink instantly in normal streams, but they also understood enough about rare natural phenomena such as tidal waves and great storms to know that water could transport heavy objects under extreme conditions. But even extreme events could not easily explain the massive granite erratics in the European Jura Mountains, especially the ones that were perched high on valley walls, far above the streams below. Compounding the problem of interpreting these deposits, however, was the fact that at a few localities in Britain, where much of the most detailed research into the ice age controversy was being conducted, the fine-grained drift that accompanied the erratic boulders contained seashells. Critics of the hypothesis that glaciers had transported erratic boulders seized on this; they claimed it was conclusive evidence that the ocean was involved. They argued that the erratics must have been transported by great, violent floods coursing over the land, and they said that there were simply no modern-day counterparts. They knew that the sea had covered parts of the continents in the past, because fossilized fish were found throughout Europe. The marine shells in “glacial” drift, they asserted, were proof that the sea had invaded the land yet again and left the drift behind when it receded. It was not until much later that the true origin of the seashells in drift was realized. James Croll, a Scottish scientist, deduced that they too had been transported by glaciers, scraped up by the ice along with sediments from the shallow seas around Britain and carried inland. However, before their origin was understood, the shells were a serious difficulty for those who argued that drift and erratics were ice age deposits.
Why does the author discuss possible effects of “rare natural phenomena such as tidal waves and great storms”?
Rhetorical Purpose Questions修辞目的题
ATo demonstrate that extreme natural phenomena were too rare to be responsible for the current locations of most erratics
BTo clarify how streams such as those in the Jura Mountains could grow large enough to transport erratics
CTo explain an early hypothesis about how erratics were transported to their current resting places
DTo emphasize that tidal waves and great storms transported erratics only in the Jura Mountains
3
Before the ice age theory was generally accepted, most geologists and naturalists argued that the erratics had been transported by water to their current resting places. They realized that even fairly small boulders would sink instantly in normal streams, but they also understood enough about rare natural phenomena such as tidal waves and great storms to know that water could transport heavy objects under extreme conditions. But even extreme events could not easily explain the massive granite erratics in the European Jura Mountains, especially the ones that were perched high on valley walls, far above the streams below. Compounding the problem of interpreting these deposits, however, was the fact that at a few localities in Britain, where much of the most detailed research into the ice age controversy was being conducted, the fine-grained drift that accompanied the erratic boulders contained seashells. Critics of the hypothesis that glaciers had transported erratic boulders seized on this; they claimed it was conclusive evidence that the ocean was involved. They argued that the erratics must have been transported by great, violent floods coursing over the land, and they said that there were simply no modern-day counterparts. They knew that the sea had covered parts of the continents in the past, because fossilized fish were found throughout Europe. The marine shells in “glacial” drift, they asserted, were proof that the sea had invaded the land yet again and left the drift behind when it receded. It was not until much later that the true origin of the seashells in drift was realized. James Croll, a Scottish scientist, deduced that they too had been transported by glaciers, scraped up by the ice along with sediments from the shallow seas around Britain and carried inland. However, before their origin was understood, the shells were a serious difficulty for those who argued that drift and erratics were ice age deposits.
Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.
Sentence Simplification Questions句子简化题
AThe fact that the most detailed research into the ice age controversy took place in Britain, where drift is fine-grained, makes interpreting the deposits difficult.
BInterpreting the deposits was a problem because most of the erratic boulders in Britain, where much research was being conducted, were accompanied by drift.
CResearch into the ice age was controversial because it took place only at a few localities in Britain where drift, boulders, and seashells appear together.
DThe presence of seashells in the drift accompanying erratic more difficult to interpret. boulders at a few localities in Britain made the deposits even
4
Before the ice age theory was generally accepted, most geologists and naturalists argued that the erratics had been transported by water to their current resting places. They realized that even fairly small boulders would sink instantly in normal streams, but they also understood enough about rare natural phenomena such as tidal waves and great storms to know that water could transport heavy objects under extreme conditions. But even extreme events could not easily explain the massive granite erratics in the European Jura Mountains, especially the ones that were perched high on valley walls, far above the streams below. Compounding the problem of interpreting these deposits, however, was the fact that at a few localities in Britain, where much of the most detailed research into the ice age controversy was being conducted, the fine-grained drift that accompanied the erratic boulders contained seashells. Critics of the hypothesis that glaciers had transported erratic boulders seized on this; they claimed it was conclusive evidence that the ocean was involved. They argued that the erratics must have been transported by great, violent floods coursing over the land, and they said that there were simply no modern-day counterparts. They knew that the sea had covered parts of the continents in the past, because fossilized fish were found throughout Europe. The marine shells in “glacial” drift, they asserted, were proof that the sea had invaded the land yet again and left the drift behind when it receded. It was not until much later that the true origin of the seashells in drift was realized. James Croll, a Scottish scientist, deduced that they too had been transported by glaciers, scraped up by the ice along with sediments from the shallow seas around Britain and carried inland. However, before their origin was understood, the shells were a serious difficulty for those who argued that drift and erratics were ice age deposits.
According to paragraph 2， which of the following was considered to be evidence supporting the idea that erratics were moved by violent floods?
Factual Information Questions事实信息题
ASediments deposited by modern-day flooding events
BKnowledge that many parts of Europe used to be under ocean water
CObservations of boulder movement in normal streams
DThe presence of very large granite erratics on valley walls above streams
5
Before the ice age theory was generally accepted, most geologists and naturalists argued that the erratics had been transported by water to their current resting places. They realized that even fairly small boulders would sink instantly in normal streams, but they also understood enough about rare natural phenomena such as tidal waves and great storms to know that water could transport heavy objects under extreme conditions. But even extreme events could not easily explain the massive granite erratics in the European Jura Mountains, especially the ones that were perched high on valley walls, far above the streams below. Compounding the problem of interpreting these deposits, however, was the fact that at a few localities in Britain, where much of the most detailed research into the ice age controversy was being conducted, the fine-grained drift that accompanied the erratic boulders contained seashells. Critics of the hypothesis that glaciers had transported erratic boulders seized on this; they claimed it was conclusive evidence that the ocean was involved. They argued that the erratics must have been transported by great, violent floods coursing over the land, and they said that there were simply no modern-day counterparts. They knew that the sea had covered parts of the continents in the past, because fossilized fish were found throughout Europe. The marine shells in “glacial” drift, they asserted, were proof that the sea had invaded the land yet again and left the drift behind when it receded. It was not until much later that the true origin of the seashells in drift was realized. James Croll, a Scottish scientist, deduced that they too had been transported by glaciers, scraped up by the ice along with sediments from the shallow seas around Britain and carried inland. However, before their origin was understood, the shells were a serious difficulty for those who argued that drift and erratics were ice age deposits.
Paragraph 2 suggests that James Croll affected the debate about the source of seashells in which of the following ways?
Inference Questions推理题
AHe helped advance the idea that the sea left the shells behind when it invaded the land and then retreated.
BHe helped people realize why the shells were a serious difficulty for geologists who argued that drift and erratics were ice age deposits.
CHe provided evidence that the shells were transported to their location at a different time than the drift and erratics were.
DHe presented a convincing argument that it was possible for glaciers to pick up seashells from the seafloor and move them inland.
6
Still, notwithstanding the seashell argument, even some of the opponents of the glacial theory had to admit that it would be impossible to transport large erratic boulders in water over long distances, no matter how violent the storm or flood. So they came up with an ingenious solution: the erratics might indeed have been carried by ice, but ice that was floating on formerly more extensive seas, transporting boulders from a northerly source. If parts of the continents had been submerged in the past, they reasoned, the icebergs could have floated over the sunken land, dropping their rocky burden as they melted. That would explain the presence of ocean shells in the drift. It was the idea of drifting icebergs that first led to use of the term “drift” for the characteristically chaotic sediments left behind by glaciers-sediments that have neither the well-defined layers nor the uniformity of grain sizes that characterize those deposited in water. The term is still in use today, although the theory that drifting icebergs deposited the seashells, erratics, and other material has been abandoned.
The word “ingenious” in the passage is closest in meaning to
Vocabulary Questions词汇题
Apartial
Blogical
Csurprising
Dclever
7
Still, notwithstanding the seashell argument, even some of the opponents of the glacial theory had to admit that it would be impossible to transport large erratic boulders in water over long distances, no matter how violent the storm or flood. So they came up with an ingenious solution: the erratics might indeed have been carried by ice, but ice that was floating on formerly more extensive seas, transporting boulders from a northerly source. If parts of the continents had been submerged in the past, they reasoned, the icebergs could have floated over the sunken land, dropping their rocky burden as they melted. That would explain the presence of ocean shells in the drift. It was the idea of drifting icebergs that first led to use of the term “drift” for the characteristically chaotic sediments left behind by glaciers-sediments that have neither the well-defined layers nor the uniformity of grain sizes that characterize those deposited in water. The term is still in use today, although the theory that drifting icebergs deposited the seashells, erratics, and other material has been abandoned.
According to paragraph 3， which of the following is NOT an accurate description of drift?
Negative Factual Information Questions否定事实信息题
AIt may contain seashells.
BIt contains grains of different sizes.
CIt is made up of well-defined sediment layers.
DIts name originated with a theory that has been abandoned today.
8
Still, notwithstanding the seashell argument, even some of the opponents of the glacial theory had to admit that it would be impossible to transport large erratic boulders in water over long distances, no matter how violent the storm or flood. So they came up with an ingenious solution: the erratics might indeed have been carried by ice, but ice that was floating on formerly more extensive seas, transporting boulders from a northerly source. If parts of the continents had been submerged in the past, they reasoned, the icebergs could have floated over the sunken land, dropping their rocky burden as they melted. That would explain the presence of ocean shells in the drift. It was the idea of drifting icebergs that first led to use of the term “drift” for the characteristically chaotic sediments left behind by glaciers-sediments that have neither the well-defined layers nor the uniformity of grain sizes that characterize those deposited in water. The term is still in use today, although the theory that drifting icebergs deposited the seashells, erratics, and other material has been abandoned.
According to paragraph 3， some opponents of the glacial theory claimed that
Factual Information Questions事实信息题
Alarge amounts of ice could have caused land to sink
Berratics were brought to their current locations by icebergs from the north
Cthe ice that transported large erratic boulders was not capable of depositing drift
Dsediments left behind by glaciers were difficult to identify
9
In the nineteenth century, scientists theorized that glaciers (ice sheets) covered much of Earth’s surface during an ancient very cold period known as the ice age. ⬛Following efforts to map ancient glaciers, researchers concluded that there had been multiple ice advances and retreats. ⬛Evidence for multiple glaciations was tied to two types of glacial deposits: one called erratic boulders, often referred to simply as erratics, and a second, glacial drift-a general term for the loose, rocky debris distributed across the countryside by slowly moving glaciers. ⬛Erratic boulders are spread over large regions in Europe and North America; the most remarkable ones are very large and they are often quite different in makeup from the local bedrock. ⬛How they got there was unknown before scientists understood how ancient glaciers transported rocks. In the northeastern United States, where there are outcrops of very distinctive rock varieties, trails of erratics of a specific type can often be traced for hundreds of kilometers, fanning out over the countryside near their sources. Careful mapping of these erratic trails can provide an accurate picture of how the glaciers that carried the boulders moved across the land.
Look at the four squaresthat indicate where the following sentence could be added to the passage
This finding suggested that there was more than just one ice age in Earth’s history.Insert Text Questions句子插入题
Where would the sentence best fit？Click on a square sentence to the passage.
10
For a long time, geologists and naturalists were uncertain about the origins of erratic boulders and loose, rocky debris found across Europe and North America.
Prose Summary Questions概要小结题
Select 3 answers
AScientists now know that streams of water from melting glaciers were once much larger and stronger than they are today and could transport boulders over long distances.
BOne popular theory was that glaclers covering large parts of North America and Europe melted, creating a great sea that moved sediments and shells across the continents.
CIt is now known that both erratics and drift were carried across the continents by glaciers that advanced over the land during the various ice ages.
DSome early scientists interpreted the discovery of seashells in drift as evidence that drift and erratic boulders were transported by ocean floods and storms.
ESome scientists argued that icebergs once floated over a large sea that covered parts of Europe and dropped boulders and drift onto the submerged land.
FBecause some characteristics of sediments deposited by glaciors appear similar to those deposited by moving water, the term “drift”is stil used to describe erratics today.
