412 



SCIENCE. 



[N. S. Vol. V. No. 115. 



the treatises here mentioned give the ma- 

 tured views of their authors, and in the case 

 of Dr. Newberry this work constitutes al- 

 most his last contribution to science. I 

 would therefore ask the privilege of direct- 

 ing the attention of those geologists who 

 are interested in the discussion of the age of 

 the Potomac formation to the opinions of 

 these two authors, and I have no apology 

 to make for quoting somewhat freely from 

 them. I will also take the liberty of itali- 

 cizing, on my own responsibility, those pas- 

 sages which I regard as bearing most di- 

 rectly upon the subject. 



"When Professor Fontaine commenced his 

 studies he was confronted by the views of 

 Professor Kogers, who, although he had rec- 

 ognized the clear distinction between the 

 Triassic formation and the higher Mesozoic 

 beds and had designated the former as 

 ' Jura-Trias' and the latter as ' Jiirasso- 

 Cretaceous,' inclined to regard the whole as 

 belonging below the Cretaceous. It there- 

 fore required paleontological evidence to 

 settle the question. Some fossil plants had 

 been found in the Trias which were deter- 

 mined by Bunbuiy, but, on account of the 

 imperfect material and of the little that was 

 then known of the Mesozoic floras, he was 

 disposed to regard them as indicating an 

 age similar to that of the Oolite of York- 

 shire. This view had been completely dis- 

 proved by Professor Fontaine's previous 

 studies of ' The Older Mesozoic,' as em- 

 bodied in his work on that flora,* and he had 

 correlated it with those transition beds in 

 Europe and other countries which lie on 

 the border of the Triassic and Jurassic and 

 are known as Ehetic. Since that work was 

 published Stur discovered at Lunz, in Aus- 

 tria, a flora which corresponds still more 

 closely with that of America, even contain- 

 ing a number of the same species, the beds 



*The Older Mesozoic Flora of Virginia. Mono- 

 graphs o£ the U. S. Geological Survey, Vol. VI., 

 "Washington, 1883. 



yielding it having been definitely fixed in 

 the Upper Keuper, and we may now look 

 upon this as the more correct correlation.* 

 After giving an account of the manner in 

 which the fossil plants of the Younger Meso- 

 zoic were discovered and of their general 

 character Professor Fontaine says (p. 14) : 

 "None of these fossils have been found in the 

 Richmond coal field, and, so far as known, 

 none of the supposed older Mesozoic areas contain 

 any of them. It is sufficient to say here that 

 this flora indicates that the Potomac beds 

 were laid down in a period decidedly more 

 recent than that in which the middle sec- 

 ondary strata of Eogers were deposited. "^ 

 Again, on p. 142, referring to the same sub- 

 ject, he says : 



" In Virginia the youngest formation 

 upon which the lower, or sandy member of 

 the Potomac is seen to rest, is the older 

 Mesozoic or Ehetic formation. The interval 

 of time, however, between the deposition 

 of the Ehetic and the deposition of the 

 Potomac beds must have been a consider- 

 able one. There are several reasons for 

 coming to this conclusion: (1) Where the 

 superposition of the Potomac on the Ehetic 

 is visible the latter is seen to have been 

 greatly worn before the deposition of the 

 former. (2) The lithologic and structural 

 character of the two formations is very 

 different, implying a total change in the 

 conditions of deposition. (3) The Ehetic 

 is made up of sandstones and shales which 

 are distinctly bedded, so that the dip and 

 strike can be easily made out. The ma- 

 terials composing these beds were well 

 sorted by water action. Before the depo- 

 sition of the Potomac the Ehetic strata 

 had been consolidated and, in the main, 

 indurated, so as to foi'm firm sandstones 

 and shales, or even slates. The Ehetic beds 

 are in many places crushed, contorted, and 

 faulted, all of which changes took place 

 before the Potomac age. No traces of them 



*Cf. Bull. Geol. Soc. Am., Vol. III., p. 31. 



