EURYPTERUS SHALES OF THE SHAWANGUNK MOUNTAINS 3OI 



It is these shale bands indicated by italics that contain the crusta- 

 cean remains. No one of them exceeds a few inches in thickness 

 and while it is not to be said that every layer has afforded fossils, yet 

 it is to be expected that each may. The most productive layers have 

 thus far proved to occur in groups as indicated on the section. 

 These shale layers are not often continuous along the bedding either 

 for the entire strike or dip of the section but they thin and pinch out, 

 reappear and continue for a short distance to again vanish ; in other 

 words they occur in a multitude of originally horizontal patches 

 over the surfaces of the sand layers. This section therefore is but 

 .a statement of variation in sediment along a given horizontal ; 

 .above or below the succession would probably vary in some meas- 

 ure. The shales carry no other fossils than the crustaceans or at 

 least none have yet been found and the sands have afforded nothing 

 in the way of fossils except a few bodies resembling in some 

 respects Arthrophycus harlani Hall (A. a 1 1 e g a n i - 

 e n s i s Harlan) which the weight of evidence brought forward 

 by the recent investigations of these problematical bodies by C. J. 

 Sarle indicates to be a worm burrow. 



The preservation of the crustacean remains in the black shale 

 is peculiar and in some respects unusually favorable for the study 

 of the smaller organisms of the fauna. The parts are altered to 

 a shining coaly film usually incrusted by a tenuous layer of pyrite 

 which when moistened brings out details of structure not other- 

 wise to be ascertained. Indications are at hand of an extensive 

 and commanding crustacean fauna. Great masses of mangled and 

 dismembered parts indicate how extraordinarily abundant these 

 Eurypterids have been, but entire individuals are great rarities. 

 The carapaces, segments and limbs afforded smooth flat surfaces 

 which have invited the process of shearing and this has usually 

 glazed the bodies and often destroyed the half of their surfaces. 

 Young forms, probably because of their size and compactness, 

 seem to have more often escaped dismemberment while larger ones 

 are represented by only an occasional fragment of striking size. 

 Heads, especially of young animals, are common but even these 

 broad shields in larger animals have been too thin to resist the 

 shearing pressure upon them. The range in size of the animals 

 bere present is worthy of especial note. We have entire animals 

 ranging from 2.5 mm to 5 mm in length, by far the smallest and 

 youngest Eurypterids yet recorded and exceedingly interesting for 

 the ontogenetic evidence they afford; and there are body segments 

 which indicate creatures of great size — that is a probable length of 



