44 The Lower Cretaceous Deposits op Maryland 



This was followed by Professor Marsh's memoir on " The Dinosaurs 

 of North America/' which contained the descriptions and figures of the 

 Maryland material collected from the iron-ore clays by J. B. Hatcher. 

 At the same time appeared Professor Ward's paper on " Some Analogies 

 in the Lower Cretaceous of Europe and America/' in which the Potomac 

 was compared with the Wealden of England, the " Scaly Clays " of Italy, 

 and the Mesozoic of Portugal. Toward the close of the year Professor 

 Fontaine's long-delayed geological paper on the Potomac appeared as a 

 Bulletin of the U, S. Geological Survey. It contained admirable de- 

 scriptions of local sections and the first geological map of the deposits, 

 covering the country between Baltimore and Petersburg. IsTo attempt 

 was made, however, to show the areal extent of the subdivisions of the 

 Potomac, and the Virginia deposits are regarded as Lower and those in 

 Maryland as Upper Potomac. Professor ISTewberry's monograph on the 

 Amboy clay flora appeared at this time as a posthumous publication un- 

 der the editorship of Arthur Hollick. 



About this time Professor Marsh published two brief papers asserting 

 the Jurassic age of the Potomac as well as of the Cretaceous beds on Long 

 Island and to the eastward. This called forth a discussion in the col- 

 umns of Science which was participated in by Arthur Hollick, L. P. 

 Ward, G. K. Gilbert, E. T. Hill, and Jules Marcou. 



In the fall of 1897 Clark and Bibbins published a full summary of the 

 results arrived at in their study of the Potomac of Maryland, dividing 

 it into four formations — the Patuxent, Arundel, Patapsco, and Raritan. 

 The two former formations were provisionally referred to the Jurassic 

 and the two latter to the Lower Cretaceous. 



In 1898 Professor Marsh replied to his critics and' reasserted the Juras- 

 sic age of the Potomac beds. 



In 1902 Clark and Bibbins published a second paper on the Potomac 

 of Maryland, in which the conclusions are essentially the same as in 

 their earlier paper. This paper was well illustrated and contained an 

 admirable map showing the areal extent of the different members of the 

 Potomac Group as developed in Maryland, the first of its kind ever 

 published. This same year the Cecil County report of the Maryland 



