0. C. Marsh — Geology of Block Island. 375 



water and shore deposits. Land plants are found in the same 

 general horizon. Marine mollusks also occur, and one charac- 

 teristic form (Nuculana) is preserved in the footprint slab. 



This specimen, although not important in itself, is worthy of 

 record as indicating the existence of an air-breathing verte- 

 brate, apparently amphibian, in the Devonian, and also as 

 offering an incentive to further exploration in the same horizon. 



Tale University, New Haven, Conn., October 16, 1896. 



Aet. LYI. — The Geology of Block Island {Continued) ; by 

 d. C. Marsh. 



The short article with the above title, in the last number of 

 this Journal (pp. 295-298), was essentially a preliminary notice 

 in the discussion of a much larger question relating to the 

 presence or absence of the Jurassic formation on the Atlantic 

 coast, a subject that I have been investigating for several years. 

 The main object was to record my own observations at a few 

 points, with the conclusions suggested, leaving a discussion of 

 the whole subject for another occasion. 



As my conclusions were so different from any that had been 

 expressed by previous writers, I thought it best to present 

 them based on my own investigations, rather than to attempt a 

 discussion of the views of all others. To have cited the 

 entire literature of the subject, extending over a century, would 

 have taken the greater part of the limited space then at my 

 command, and seemed hardly necessary. 



Since my article was published, I have had further oppor- 

 tunity to follow out the investigation in several directions, and 

 hope soon to place these results, also, on record. I may say 

 here, however, that an examination of both the Raritan and 

 Staten Island clay deposits has supplied two links in a chain of 

 evidence, that I had not before known from personal observa- 

 tion. This chain now extends from the Potomac River to 

 Martha's Vineyard, along the natural line of the Jurassic 

 horizon, and indicates the Jurassic age of this series of strata 

 beyond reasonable doubt. 



Many and various opinions have been expressed as to the 

 geological age of this series of strata, especially of the clays 

 east of the Hudson River which are here under consideration. 



The brilliant, variegated cliffs of Gay Head seem to have 

 first attracted the attention of both mariners and geologists, 

 and descriptions of their geological features began more than 

 one hundred years ago. In 1786, Samuel West and William 

 Baylies together explored Gay Head, and separately recorded 

 what they saw, in vol. ii, Memoirs of the American Academy 

 of Arts and Sciences, 1793. They discovered the bones of 



