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) 'Traité de Paléontologie Végétale.' Schimper. (37) 'Histoire des Végétaux Fossiles.' Brongniart. (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.