508 A. W. GRABAU PALEOZOIC DELTA DEPOSITS OF NORTH AMERICA 



ture and adolescent individuals, the younger growth stages prevail in the 

 Shawangunk grit shales and .large individuals are represented only by 

 fragments, which indicate that they may have been destroyed by the more 

 turbulent water conditions." 105 



In the middle portion of the Shawangunk conglomerate of the Dela- 

 ware Water Gap sections similar black shales have furnished Eurypterids. 

 These were discovered by Mr. Paul Billingsley, of Columbia University, 

 who collected a large amount of material. Prof. Gilbert Van Ingen and 

 Mr. J. C. Martin also obtained material from this horizon, from which 

 Clarke and Euedemann were enabled to recognize numbers 1,3, 7, 9, and 

 10 of the list of species found in the Shawangunk of Otisville. Mr. Bil- 

 lingsley reports 106 that the fragments are all dissociated, the carapaces 

 commonly occurring by themselves and dissociated from the abdominal 

 segments, as if rearranged by violent currents. 



Upper Siluric or Monroan. — The Upper Siluric, both in this country 

 and in Europe, shows the best and most typical development of the 

 Eurypterids. In the Lower Monroan (Put-in-Bay dolomite), a marine 

 formation, occurs one species, Euryptems eriensis Whitfield (=E. mi- 

 crophthalmias Hall, according to Clarke and Euedemann), but there are 

 only a few dissociated carapaces and one abdomen. Associated with these 

 in the same bed are small brachiopods (Spirifer, etcetera). The Bertie 

 water-lime of Upper Monroan age contains the largest number of species 

 of any one formation in the world, namely, thirteen 107 species, referred to 

 the five genera: Eurypterus (5 species), Pterygotus (4 species), Eusar- 

 cus (1 species), and Dolichopterus (3 species). The specimens are for 

 the most part wonderfully well preserved, but other organisms are ex- 

 tremely rare. In the Museum of the Buffalo Society of Natural Sciences 

 occur a few specimens of marine organisms obtained from the formation 

 which has furnished the Eurypterids. These are two specimens of a long, 

 slender Orthoceras (0. undulatum), but the fossils are crushed, jnacer- 

 ated, and more or less worn, and they were apparently brought into the 

 Bertie deposits from outside marine waters. The whole aspect of the 

 fossils shows that the animals did not live where the remains are found. 

 Associated with these are a number (six) of well preserved shells, which 

 have been described as Biscina grandis. These, hoAvever, belong to the 

 genus Hercynella, a pulmonate gastropod which may as readily be re- 

 ferred to fresh as salt water. On a large number of the slabs containing 



105 Clarke and Ruedemann, loc. cit.. p. 105. 



106 Manuscript deposited in Columbia University. 



107 The original number described was 23. but many of these have been shown by 

 Clarke and Ruedemann to be synonyms of other species. 



