FLUKA OK OLDKK POTOMAC l'X)HMAT10.N. 395 



Professor Maisti's ,a:eii('r:il claim thai ihc Wcaldcii sliould he referred lo 

 down the Jurassic. 



In oi-der still further to emphasize the wide difference between the 

 ( )ld('r and \ewei- Potomac, and also to jiive the views of Professor Fontaine, 

 who liad most fully studied the foi-mei', and of Doctor Newliei'iy, who was 

 at the time of his death the first authoi'ity on the laltei', I made a second 

 conti'iliution" in the spriufj; of ISO", (juoting somewhat extensively fi'om 

 those authors, and endeavoring to show that Doctor Newberry placed 

 the Amboy clays somewhat too high, while Pi'ofessor Marsh placed them 

 much too low and confounded them with the Older Potomac. 



Professor Clark and Mr. Bibbins pul;)lished in August, 1897,'' a some- 

 what full account of the I'esults at wliich they had arrived in their study 

 and preliminary survey of the Potomac foi'iuation in Maryland. Thev 

 admit the great difference between the age of the lower and the upper 

 beds, and sustain the view which I maintained in my paper on the Potomac 

 formation in ISOo, that it consists of a series of beds clipping coastward and 

 beveled on the surface, so that in crossing the belt from northwest to 

 southeast one I'ises in the geological scale from the lowest to the highest 

 beds; in other words, that the Potomac formation is not a "trough," as 

 was formerly supposed, but an integral part of the sedimentary beds that 

 make up the coastal plain. They did not, however, accept the nomen- 

 clature that I proposed, but adopted an entirely different one, making four 

 instead of six subdivisions, which in ascending order are as follows: 

 Patuxent, Arundel, Patapsco, Raritan. On page 481 they say: 



It i.s the conclusion of tiic authors, founded upon a detailed stratigrapliic study 

 of the Potomac jiroup, tiiat all the beds which have afforded dicotyledonous types of 

 plant hfe are above those wliich have yieldetl the vertebrate remains, and, moreover, 

 that a marked unconformity exists between the two series of deposits. The evidence 

 for this conclusion will be brought out in the succeeding pages. 



This was an inference only, and has been disproved by the study of 

 the plants that had l)een already collected. The Patuxent formation is 

 descril)ed as follows: 



The deposits of the Patuxent formation consist nniinly of sand, at times (juite 

 j)ure and gritty, but generally containing a considerable amount of kaolinized feld- 



« Professor Fontaine and Doctor Newberry on tlie age of tlie Potomac formation: Ibid., Marcli r2, 

 1897, pp. 411-423. 



'' The stratigraphy of tlie Potomac group in Maryland, by Wni. Bullock Clark and Artluu- Bihhins: .Tourn. 

 Oeol.. Vol. V, No. .5, July-August, 1897, pp. 47\)-5&>. 



