Elements of geology, or, The Elements of geology, or, The ancient changes of the earth and its inhabitants as illustrated by geological monuments elementsofgeolog00lyel Year: 1868 Aticula incequwalvis, Sow. Lower Oolite, and Lias. . Avicula cygnipes, Phil. Lias, Gloucestershire and Yorkshire. The peculiar aspect which is most characteristic of the Lias in England, France, and Germany, is an alternation of thin beds of blue or gray limestone, having a surface which becomes light-brown when weathered, these beds being separated by dark-colored, narrow argillaceous partings, so that the quarries
Elements of geology, or, The Elements of geology, or, The ancient changes of the earth and its inhabitants as illustrated by geological monuments elementsofgeolog00lyel Year: 1868 Aticula incequwalvis, Sow. Lower Oolite, and Lias. . Avicula cygnipes, Phil. Lias, Gloucestershire and Yorkshire. The peculiar aspect which is most characteristic of the Lias in England, France, and Germany, is an alternation of thin beds of blue or gray limestone, having a surface which becomes light-brown when weathered, these beds being separated by dark-colored, narrow argillaceous partings, so that the quarries of this rock, at a distance, assume a striped and riband-like aspect.* The Lias has been divided in England into three formations, the Upper, Middle, and Lower. The Upper Lias consists first of sands, which were formerly regarded as the base of the Oolite, but which, according to Dr. Wright, are by their fossils more properly refer- able to the Lias; secondly, of clay shale and thin beds of limestone. The Middle Lias, or marlstone series, has been divided into three zones; and the Lower Lias, according to the labors of Quenstedt, Oppel, Strickland, Wright, and others, into six zones, each marked by its own group of fossils. This Lower Lias averages from 600 to 900 feet in thickness. From Devon and Dorsetshire to Yorkshire all these divisions, ob- serves Professor Ramsay, are constant; and, from bottom to top we cannot assert that anywhere there is actual unconformity between any two subdivisions, whether of the larger or smaller kind. In the whole of the English Lias, there are about 243 genera, and 467 known spe- The whole series has been divided by zones^ characterized by particular ammonites; for while other families of shells pass from one division to another in numbers varying from about 20 to 50 per cent., these cephalopods are almost always limited to single zones, as Quenstedt and Oppel have shown for Germany, and Dr. Wright for England. J As no actual unconform
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