NORTH AMERICAN GEOLOGY. 201 



36. Younger Mesozoic. — The age of the Xew Jersey clays and marls has 

 been briefly discussed by Cook,* Whitfield, t and Xewberry.^ The lat- 

 ter considers the mnrls equivalent to the chalk of Europe and the 

 marine Cretaceous of Colorado. Whitfield sees no reason to "dispute 

 the notion generally held that the lower marl bed of the State is 

 equivalent to 'No. 4,' or the Fort Pierre group of the Upper Missouri." 

 Newberry states his o[)inion that the Earitan clays are at the horizon 

 of the upper greensand of Europe and the Dakota of the West ; an 

 opinion shared by Cook. Whitfield thinks the fauna is in some re- 

 spects allied to that of the Jura, and is inclined to consider the group 

 the Eastern representative of that formation. 



37. McGee, in a paper on the geology of Washington and vicinity, de- 

 scribes the newer Mesozoic, whieh occupies a wide area in that district 

 and is there called the Potomac formation. The ujiper part is made 

 up of highly colored clays, with sand and gravel ; the lower part is 

 sand and gravel, with intercalations of clay. Stratification is often ab- 

 sent, and the materials are sometimes intermingled. The formation 

 appears " to consist of inosculating deltas of the Potomac and other 

 Atlantic-coast rivers and the littoral deposits into which they merge, 

 laid down along a bay-indented coast upon a highly inclined and irreg- 

 ular sea-bottom, produced by combined depression and seaward tilting 

 of a deeply corraded surface in late Jurassic or early Cretaceous time."§ 

 Newberry considers the Potomac formation Neocomian in age. 



PALEOZOIC OF EASTERN NORTH AMERICA. 



3'>. President Dawson, in his address before the British Association, 

 discussed the origin of the American Paleozoic sediments, and stated 

 his preference for the theory that they were derived from Arctic 

 lands and deposited similarly to the great sand banks of the Atlantic 

 coast. Hull. II in a letter to Nature, opposes this idea on the ground of 

 the character of the deposits and the inadequacy of the currents, 

 especially if tliere was no coast to determine their course. He restates 

 his opinion that the sediments were deposited off-shore from a very 

 wide land surface in the region of the present Atlantic Ocean, " toward 

 which the sediments thicken, and opposite to that in which the lime- 

 stones are most developed."^ Dana** and Le Conteft disagree with 

 Dawson and Hull in considering the Paleozoic land surface to have 



* Branchiopoda aud Lamellibrancliia of the Raritau Clays aud Greeusaud Marls 

 of New Jersey, by Whitfield, pji. ix-Xlli. 



i Ibid., pp. xvi-xx. 



t New York Acad. Sci., Trans., vol. 5, pp. 18-19. 



§ District of Columbia, Report of Health Officer for 1885, pp. 19-21, aud Am. Jour. 

 Sci., Ill, vol. 31, pp. 473-474. 



II Canadian Record Science, vol. 2, pp. 201-228, 265-285, aud elsewhere, 



1[ Vol. 34, p. 496. 



** Am. Jour. Sci., in, vol. 32, pp. 407-4C8. 



ttGeql. Magazine, vol. 3, pp. 97-101 and 189-190. 



