516 A. W. GRABATJ PALEOZOIC DELTA DEPOSITS OF NORTH AMERICA 



This latter was originally considered Lower Trenton, then Black River, 

 and finally Upper Chazy. I have elsewhere 116 discussed the age-relations 

 of the Normanskill, and have shown that its equivalency must be with 

 the transgressional portion of late Chazyan (including Black River) 

 time. This is of interest, in view of the fact that the Eurypterids of the 

 Schenectady beds are close relatives of the Eurypterids of the Norman- 

 skill, there being at least in one case specific identity. These occurrences 

 Clarke says represent "... a purely marine basin, where sedimenta- 

 tion went on rapidly in an Appalachian depression." 117 . . . It will 

 at first glance seem that we have here an undoubted marine occurrence, 

 but closer inspection reveals the fact that all is not as satisfactory as it 

 might be. By the courtesy of the State paleontologist, I was permitted 

 to view the collection of the Schenectady Eurypterids, and I was espe- 

 cially struck with the fragmentary character of the exoskeletons, since 

 illustrated in the magnificent memoir on the Eu^pterids. Plenty of 

 carapaces and abdominal segments and separate leg parts occur, and now 

 and then a number of body segments in conjunction, but not a whole 

 individual was to be seen. The Normanskill material is equally frag- 

 mentary; ". . . few legs and telsons have been found in connection 

 with the carapaces and fragmentary abdomina." 11S 



This is certainly remarkable, in view of the fact that the Eurypterids 

 occur entire elsewhere, and that entire specimens of Triarthrvs becki are 

 found. Certainly we can deal here only with cast-off exoskeletons which 

 were dismembered and not with buried entire individuals. Where were 

 the individuals that furnished these exoskeletons ? A significant fact lies 

 in the greater rarity of these fossils in the black mud, where they are 

 better preserved than in the sandy beds. This is equally true of the 

 Normanskill and of the Schenectady beds. The sandy beds certainly 

 represent shore-derived elastics, and indicate a stronger supply of terrig- 

 enous detritus and swifter river currents than is the case with the muds. 

 In the Normanskill beds there is distinct evidence of shallow water in the 

 conglomeratic beds, full of what appear to be mud pebbles, and in the 

 wave-marks and winnows of comminuted seaweeds with the Eurypterids 

 in the troughs. That the fragments should be most abundant when the 

 lithic character of the rock suggests the greatest inrush of land waters 

 carrying detritus is certainly a most significant fact. It seems to point 

 directly to the land waters as the source of these fragments. It is hard 

 to escape the conclusion that we are dealing with material rafted from 



ue Outlines of Geological History Symposium, p. 56 ff. 



"< 7 Loc. cit, p. 31. 



U8 Clarke and Ruedemann, loc. cit., p. 413. 



