146 



SCIENCE. 



[N. S. Vol. VIII. No. 188. 



mation on the Atlantic Coast.'* In this 

 paper I brought together the results of a 

 careful investigation which I had been con- 

 ducting for several years, going to prove 

 that the Jurassic formation, generally sup- 

 posed to be wanting on the Atlantic border, 

 was represented bj' a definite series of strata 

 in the exact position where such deposits 

 were to be expected. Accompanying this 

 communication, I exhibited a number of 

 drawings and sections illustrating the Ju- 

 rassic deposits of the West, which I had 

 long before investigated and fully described, 

 namely, the Baptanodon beds, consisting of 

 marine Jurassic strata with many charac- 

 teristic fossils, mostly invertebrates, and 

 above these the fresh- water Atlantosaurus 

 beds, which have yielded such vast numbers 

 of gigantic reptiles and other characteristic 

 vertebrates. Sections showing the relative 

 positions of these deposits, with the strata 

 above and below them as they are seen in 

 several localities in Wj'oming and Colorado, 

 were also exhibited. 



In comparison with this great develop- 

 ment of the Jurassic in the West, I next 

 discussed the so-called Potomac formation 

 in Maryland, in which I had found a corre- 

 sponding vertebrate fauna that proved the 

 strata containing them to be also of Jurassic 

 age. I then gave a brief account of vay re- 

 searches during that season, in following 

 essentially the same strata to the eastward 

 through Delaware and New Jersey, and 

 likewise presented evidence showing that 

 apparently the same Jurassic beds were to 

 be found in position beneath Long Island, 

 Block Island and Martha's Vineyard, repre- 

 sented by the variegated basal clays of 

 these islands, which had previously been 

 supposed to be of much later age. The 

 evidence seemed conclusive that in this 

 series we had remnants of an extensive 



* Science, Vol. IV., p 805, December 4, 1896. See 

 also American Journal of Science, Vol. II., p. 295, 375 

 and 433, 1896. 



formation of fresh-water origin, the strata 

 consisting mainly of soft sandstones and 

 plastic clays of great thickness. In their 

 physical characters, and especially in their 

 variegated brilliant colors, these deposits 

 differed widely from any others known on 

 the Atlantic border, and were only equalled 

 in this respect by the Jurassic beds of the 

 Rocky Mountain region. The presence on 

 the Atlantic coast of such an extensive 

 formation, with its massive beds of plastic 

 clay, all of fresh- water origin, clearly proved 

 the former existence of a great barrier be- 

 tween the basin in which these clays were 

 deposited and the Atlantic Ocean, a barrier 

 that has long since disappeared through 

 subsidence, or was broken down by the 

 waves of the Atlantic, which are still rap- 

 idly removing the remnants of the formation 

 along its eastern exposure, as may be seen 

 on Block Island and at Gay Head on Mar- 

 tha's Vineyard. 



In discussing the age of this formation, 

 its position above the Triassic and below 

 the marine Cretaceous, its characteristic 

 physical characters, distinct from those 

 above and below, and its western extension 

 into the strata of undoubted Jurassic age 

 in the Potomac beds of Maryland, all 

 pointed to the conclusion that its members 

 belong to the same general epoch and were 

 deposited during Jurassic time, 



In the paper thus cited I confined myself 

 strictlj' to the Potomac formation north of 

 the Potomac River, and •what I believed to 

 be its eastern extension as far as Martha's 

 Vineyard, all of which I had personally ex- 

 plored. I particularly avoided any discus- 

 sion of the so-called Potomac beds south of 

 the Potomac River, although I had been 

 over these deposits at various points along 

 the Atlantic border and around the Gulf as 

 far as the Mississippi River. I closed the 

 paper with the promise of taking up that 

 part of the subject later. 



As the question was a difficult one and 



