The Ancient Life History of the Earth eBook

Henry Alleyne Nicholson
This eBook from the Gutenberg Project consists of approximately 391 pages of information about The Ancient Life History of the Earth.
     Dolomitic Conglomerate of the Bristol Area”—­’Quart.  Journ. 
     Geol.  Soc.,’ vol. xxvi., 1870.  R. Etheridge, sen.
(31) “Remains of Labyrinthodonta from the Keuper Sandstone of
     Warwick”—­’Quart.  Journ.  Geol.  Soc.,’ vol. xxx., 1874 Miall.
(32) ‘Manual of Geology.’  Dana. (33) ‘Synopsis of Extinct Batrachia and Reptilia of North America.’ 
     Cope.
(34) ‘Fossil Footmarks.’  Hitchcock.
(35) ‘Ichnology of New England.’  Hitchcock.
(36) ‘Traite de Paleontologie Vegetale.’  Schimper.
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(38) ‘Monographie der Fossilen Coniferen.’  Goeppert.

CHAPTER XVI.

THE JURASSIC PERIOD.

Resting upon the Trias, with perfect conformity, and with an almost undeterminable junction, we have the great series of deposits which are known as the Oolitic Rocks, from the common occurrence in them of oolitic limestones, or as the Jurassic Rocks, from their being largely developed in the mountain-range of the Jura, on the western borders of Switzerland.  Sediments of this series occupy extensive areas in Great Britain, on the continent of Europe, and in India.  In North America, limestones and marls of this age have been detected in “the Black Hills, the Laramie range, and other eastern ridges of the Rocky Mountains; also over the Pacific slope, in the Uintah, Wahsatch, and Humboldt Mountains, and in the Sierra Nevada” (Dana); but in these regions their extent is still unknown, and their precise subdivisions have not been determined.  Strata belonging to the Jurassic period are also known to occur in South America, in Australia, and in the Arctic zone.  When fully developed, the Jurassic series is capable of subdivision into a number of minor groups, of which some are clearly distinguished by their mineral characters, whilst others are separated with equal certainty by the differences of the fossils that they contain.  It will be sufficient for our present purpose, without entering into the more minute subdivisions of the series, to give here a very brief and general account of the main sub-groups of the Jurassic rocks, as developed in Britain—­the arrangement of the Jura-formation of the continent of Europe agreeing in the main with that of England.

I. THE LIAS.—­The base of the Jurassic series of Britain is formed by the great calcareo-argillaceous deposit of the “Lias,” which usually rests conformably and almost inseparably upon the Rhaetic beds (the so-called “White Lias"), and passes up, generally conformably, into the calcareous sandstones of the Inferior Oolite.  The Lias is divisible into the three principal groups of the Lower, Middle, and Upper Lias, as under, and these in turn contain many well-marked “zones;” so that the Lias has some claims to be considered as an independent formation, equivalent to all the remaining Oolitic rocks.  The Lower Lias (Terrain Sinemurien

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The Ancient Life History of the Earth from Project Gutenberg. Public domain.
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