360 Prof. Sedgwick 071 the Classification of the Strata [^May, 



the formation. The whole thickness of the alum-shale is proba- 

 bly not much less than 1000 feet. 



The fossils of the formation are too well known to require any 

 description. It contains ferns and impressions of fish, at least 

 very much resembling those which are found in the lias of the 

 Dorsetshire coast. There are imbedded in it many remains of 

 the Ichthyosaurus; and throughout its mass are specimens innu- 

 merable of the gryphcca incurva and of other characteristic lias 

 fossils. Moreover it does not, I believe, contain a single speci- 

 men of the most characteristic fossils, either of the Oxford clay, 

 or of the Kimmeridge clay. If, therefore, strata are to be iden- 

 tified by their imbedded remains, the alum-shale is the true 

 representative of the lias. 



Again, the alum-shale in Yorkshire appears precisely in the 

 same situation in which the lias is generally found in its range 

 across our island ; viz. at the base of the great terrace which 

 overlooks the plain of the new red sandstone. Lastly, it is 

 grouped in the same manner as the Has. This will be evident 

 by comparing the previous statements with the sections given 

 in the " Outlines of the Geology of England," p. 262, 263. 

 How the conclusion which seems to follow from all these facts 

 is to be avoided, I am at a loss to understand. It may be said 

 that the alum-shale is thicker than the lias formation, and that 

 it contains much less calcareous matter. But the same remark 

 would exclude the shale beds at Lyme, in Dorsetshire, from this 

 formation, — a conclusion which cannot be admitted, inasmuch 

 as the argillaceous cliff of Lyme is surmounted by the inferior 

 ooUte and forest marble, and, therefore, cannot be mistaken.* 

 Sect. 8. — New Red Sandstone and Magnesian Limestone, Sfc. 

 It is unnecessary in this place to mention the various indica- 

 tions of the new red sandstone formation in the plains of Cleve- 

 land, or in the bed of the Tees. In following the line of coast, 

 it first appears near the mouth of the river (a little above West 

 Coatham), in its most characteristic form, associated with veins 

 of gypsum. North of the Tees, it is at Hartlepool succeeded by 

 the magnesian limestone. The sections on the coast do not 

 distinctly show the order of superposition ; but the general dip 

 of the beds in the whole district and their relative position, would 

 lead us to conclude that the magnesian limestone was the lowest 

 of the two formations above-mentioned, and that both were infe- 

 rior to the alum-shale. The fact, however, does not admit of 

 any doubt ; for it is well known that the two formations run 

 together to the central parts of the island, and preserve the same 

 constant relations to each other, and to the beds above them. 



• Jlr. Smith, as has been stated above, identifies the alum-shale with the Oxford clay. 

 In dissenting from such an authority, I cannot refrain from expressing my admiration 

 of the incomparable labours by which he has laid the foundation of all that is accurately 

 known respecting the aiTangeraent of our secondary strata. 



