444 Marsh — Jurassic formation on the Ailantio Coast. 



This eminent geologist also referred to the Jurassic certain 

 silicious, argillaceous, and pebbly beds in Virginia and further 

 north, as possibly " a passage-group analogous to the Wealden 

 of British geology."^ P. T. Tyson in 1860 referred the Mary- 

 land clays to the Cretaceous, and later to the Jnrassic.f 



Long before this, in 1835, H. D. Rogers, in his sketch of the 

 geology of l^orth America, clearly recognized what is here 

 regarded as Jurassic as pertaining to one great formation. He 

 described this as extending along the tide water plain of the 

 Atlantic, from the Carolinas through Yirginia, Maryland, 

 Delaware, Pennsylvania, and [N'ew Jersey, and also as continu- 

 ing on through Long Island to Martha's Vineyard and ISTan- 

 tucket. He gave it the name of " Ancient Alluvium," but 

 included in it the plastic clay formation and part of the Gay 

 Head deposits, the latter of which he considered Cretaceous.^ 



The next noteworthy description of the Jurassic as here 

 defined was given by J. C. Booth in his report on the Geo- 

 logical Survey of Delaware, 1841. He described the varie- 

 gated plastic clays of that state, and gave to them the name of 

 " Red Clay Formation," which he regarded as belonging to the 

 Upper Secondary. The more recent publications on this Atlantic 

 Coast formation are well known, and need not be cited here. 



Among the early explorers who contributed to our knowl- 

 edge of the Jurassic of the Rocky Mountains and Pacific coast 

 region were J. Marcou, in New Mexico, 1853 ; C. King, in 

 California, 1863 ; and, in the same state, W. Gabb, 1864, 

 and F. B. Meek, 1865. 



The earliest discovery of the Jurassic in the Arctic region 

 of this country was by Sir E. Belcher, in 1852, who found 

 remains of Ichthyosaurus on Exmouth Island. The latest 

 information in regard to the Jurassic comes also from the 

 Arctic region, where Nansen has found this formation contain- 

 ing many fossils, near Franz Joseph Land. 



Jura- Trias. 



The term Jura-Trias now in use is in reality a confession of 

 ignorance, excusable, perhaps, a quarter of a century ago, but 

 unpardonable now in those whose duty it is to map or define 

 the formations of this country. Yet this term is still some- 

 times used for so clean-cut a Triassic horizon as the Connecticut 

 River sandstone. It is true that in early days of JNew England 

 geology, this formation was in part referred to the Jurassic, 

 but at the present time no one at all familiar with the evidence 

 of the abundant vertebrate life found in it could make such 

 a mistake. This is equally true of the southern extension 

 of the same formation along the Atlantic coast, where it is 

 everywhere quite distinct from the Jurassic. In the West, 

 the dividing line is less marked in some regions, but I believe 

 that even there careful explorations alone are required to 

 separate these two allied formations. 



* Proceedings Boston Society, vol. xviii, pp. 104, 105, 18*75. 



f 1st Report State Chemist, Maryland, p. 41, 1860 ; 2d Report, p. 54, 1862. 



:}: Report British Association, Edinburgh Meeting, pp. 1-66, 1835. 



