80S 



SCIENCE. 



[N. S. Vol. IV. No. 101. 



representative of the Jurassic, let us see 

 what follows. The authorities on this for- 

 mation — McGee, Ward, Fontaine, Uhler 

 and others — agree that it extends south 

 along the Atlantic border as far as North 

 Carolina, holding the same relative position 

 and the same general characteristics. That 

 it also extends west around the Gulf border 

 has been asserted by those most familiar with 

 its southern development, but on this point 

 I cannot speak from personal observation. 

 • From the Potomac Eiver northward, 

 however, I have made sufficient explora- 

 tions along its outcrops through Maryland, 

 Delaware and Pennsylvania, to the Dela- 

 ware River, to ascertain its distinctive 

 features, essentially the same throughout, 

 with its geological position still maintained. 

 In New Jersey I have likewise followed its 

 equivalent strata across the State in the 

 great series of variegated plastic clays, to 

 the Raritan River, and again in their ex- 

 posure on Staten Island, everywhere seem- 

 ingly the same series of strata and of the 

 same age. The position is a definite one, 

 always along the line where the Jurassic 

 must lie, if present. 



Along the northern shore of Long Island, 

 the same formation extends, and at many 

 outcrops it may be seen with its character- 

 istic features well displayed. I have re- 

 cently examined these exposures at many 

 points, and all tell the same story. At 

 Montauk Point and on Gardiner's Island 

 I found apparently the same deposits, but 

 with local variations that need not now be 

 discussed. 



Block Island, evidently once a part of 

 Long Island, I have also examined. Its 

 basal clays agree in most respects with the 

 above representatives of the same horizon, 

 as I have shown elsewhere.* 



* American Journal of Science, Vol. II., p. 295, 

 October, and p. 375, November, 1896. In the second 

 paper will be found an abstract of the more important 

 literature. 



GAY HEAD. 



By far the finest exhibition of the great 

 formation in question may be seen on 

 Martha's Vineyard, especially at Gay Head, 

 which for a century has attracted the at- 

 tention of geologists, who have tried in vain 

 to solve its mysteries. My first visit to 

 this classic region was in September last, 

 and I know of no point on the Atlantic 

 coast, from Nova Scotia to Florida, of more 

 interest to geologists. The striking resem- 

 blance between the variegated cliffs at Gay 

 Head, the Potomac hills in Maryland, and 

 Como bluffs in Wyoming, will impress 

 everyone who has seen them. That all 

 three are of essentially the same geological 

 age, I have good reason to believe. Two of 

 them are certainly Jurassic, as demon- 

 strated by typical vertebrate fossils, and I 

 hope soon to prove that Gay Head, so simi- 

 lar in all other respects, also contains the 

 same characteristic vertebrate fauna that 

 marks the Jurassic — the long missing for- 

 mation on the Atlantic coast. 



It has already been shown that the verte- 

 brate fossils of the Potomac in Maryland 

 prove its age there to be Jurassic, especially 

 when taken in connection with the rich 

 fauna of the Atlantosaurus beds of the 

 West. In determining the age of the whole 

 series, every aid that paleontology can ren- 

 der should be brought to bear upon the 

 question, but a discrimination greater than 

 has hitherto been shown is necessary to 

 secure the best results. 



In addition, then, to the evidence of 

 vertebrate fossils as to the age of this east- 

 ern formation, the testimony of the inverte- 

 brates and plants should also be considered. 

 The invertebrates known from these strata 

 are few in number, but some of the mollusks 

 among them point to the Jurassic age, as 

 Whitfield has shown.* Nearly all, how- 

 ever, were estuary or fresh-water forms, 

 which are now generally admitted to be of 



* Monograph IX., U. S. Geol. Survey, p. 23, 1885. 



