130 PEOCEEDINGS OF THE GEOLOGICAL SOCIETY. [Feb. 5, 



tions of one region are represented by shales and sandstones in 

 another ; but the point I wish to urge particularly is that such con- 

 temporaneous strata are necessarily developed from opposite direc- 

 tions, and that the region over which one of these classes of strata 

 is most fully represented is that in which the other has been most 

 sparingly deposited. Thus the White Chalk of Europe is replaced 

 by sandstones, shales, and lignite in America*, in which there is very 

 little calcareous matter. We may therefore behave that a clear ocean, 

 uncontaminated by muddy sediment, overspread the greater part of 

 Europe, while the waters of North America were charged with sedi- 

 ment. The cause of the change of mineral character is here sufficiently 

 evident. The animals which flourished in the clear waters of Europe, 

 and by whose vital powers the soluble calcareous matter was con- 

 verted into chalk, were incapable of living where the sea was turgid. 

 In this case the animals were Corals, Sponges, Bryozoa, Cytherldce, 

 and Foraminifera. 



(c.) Confining our view to narrower limits, let us take for another 

 illustration the Great OoHte as it occurs in Oxfordshire and on the 

 east coast of Yorkshire. In Oxfordshire the most conspicuous member 

 is the " White Limestone " (not unlike hardened chalk), interposed 

 between the Stonesfield Slate series t and the Porest-marble. The 

 White Limestone is generally very free from any admixture of sand 

 or clay, and is essentially organic in its composition. On the other 

 hand, the Forest-marble and Stonesfield Slate contain a large admix- 

 ture of sedimentary ingredients ; but neither of them is as thick as 

 the White Limestone. Yet, when traced to the coast-section of Scar- 

 borough, a great change is found to have taken place in the relative 

 development of these three members of the Great OoHte. The 

 lowest and highest members have expanded by an accession of sedi- 

 mentary materials. They are (as it seems to me) the "lower" and 

 *' upper sandstone and shale series," stated by Prof. Phillips to be 

 700 feet in thickness (but possibly more), while the central calca- 

 reous member has become so thin and debased as to be scarcely re- 

 cognizable. 



(c^.) We may also instance the Permian Rocks of England. Thus 

 we find the calcareous members attaining their maximum development 

 of 500 feet according to Prof. Sedgwick, or 600 feet according to Mr. 

 Kirkby, in Durham, dwindling to 440 feet in South Yorkshire ; and 

 when last exposed towards Nottingham, showing evident symptoms of 

 debasement. Over these districts the Lower Permian strata are but 

 sparingly represented, but as we proceed south-westward are found 

 gradually to augment, till in Warwickshire and Salop they attain their 

 full thickness of 1500 or 2000 feet, the whole of which is formed of 

 sandstones, shales, breccias, and conglomerates. It will be observed 

 that the points of maximum development of the calcareous and sedi- 



^ Lyell's Manual of Elem. GeoL, 5th edit. p. 265 ; Br. Hector, Quart. Journ. 

 Geol. Soc. vol. xvii. p. 412, &c. 



t In the Memoirs of the Geological Survey, 1858, the White Limestone is 

 called "the Upper Zone," and the Stonesfield Slate "the Lower Zone" of the 

 Great Oolite. 



