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Page:Popular Science Monthly Volume 54.djvu/279

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first described as horsebacks in Maine, about seventy of them having been described in the report of 1861 and 1862. It was not till after the description of the Swedish O̊sar that the nature of these lines or ridges was understood; and now they were found in every prominent valley in New England, as attendant upon the recession of the ice sheet. Professor Hitchcock gave the correct name of these ridges in his Elementary Geology, 1860; while for many years subsequently they were erroneously called kames, even in the geology of New Hampshire.

Professor Hitchcock gave the name of Champlain to the fossiliferous clays associated with the till of the Atlantic coast. The term has come into general use as connected with the melting of the ice in the latter part of the period. Because of the presence of boreal species, and of analogies with similar deposits in Europe, Professor Hitchcock has asked the question whether there may not have been a Champlain glacial epoch posterior to those named farther in the interior of the country, the Kansan, Iowan, and Illinoisian epochs.

Those who explore the geology of northern New England have to deal with crystalline rocks of various ages, and the opinions of our best geologists have not been in agreement respecting them. Professor Hitchcock was the first to make a geological map of New Hampshire, and he also demonstrated the anticlinal nature of the Green Mountains of Vermont. His teachers had inculcated the view that these eminences belonged to a synclinal disposition, coupling this with theoretical assertions as to their age and metamorphism. Finding their main principle to be erroneous, he naturally disparaged their theories, though more recent studies are eliminating many of the schists from the Archæan. All the later explorers in the field—Canadians and members of the Geological Survey—accept a pre-Cambrian anticlinal in the heart of the Green Mountains.

The distribution of the New Hampshire formations was made out for the most part before any assistance was derived from the labors of Dr. G. W. Hawes and other petrographers. Twenty years ago, at the date of the final publication of the New Hampshire maps, the doctrine of an igneous origin of the crystalline schist had hardly been hinted at. What seems elemental to the modern petrographer who has acquired his technical education since 1890 was unknown then, and the classification given in the report may not agree with that now taught. In the midst of the diverse views entertained, Professor Hitchcock classified the rocks of northern New England according to this principle: rocks that are identical in petrographical composition are assumed to have had the same origin, and to be synchronous. Professor Hitchcock was almost the first of American geologists to employ the petrographer as a help to the understanding of the crys-