DISTRIBUTION AND OCCURRENCE OF EURYPTERIDS 517 



the land and deposited near the seashore. It is not impossible that the 

 so-called sea<*weed Sphenothallus, which also appears to be abundant in 

 the Normanskill beds, was a land or fresh- water plant; its occurrence in 

 these same beds is not without significance. The presence of Graptolites 

 might at first suggest that the black muds were of deep-water origin, but 

 such is not necessarily the case. The Graptolites are generally fragments, 

 and might just as readily have been cast up onto a mud-flat surface as 

 hydroids at the present time are cast up on mud flats which are exposed 

 to the air often for long periods. The shales may just as readily have 

 constituted the submerged portion of a delta or confluent series of deltas, 

 which received drainage on the one hand from the land and on the other 

 was covered by the wash of the sea. These shales occasionally show mud 

 cracks, indicating that they accumulated in shallow water. 



If land derived, the Eurypterid fragments of the Normanskill and 

 Schenectady beds must have been washed into the Ordovicic Sea before 

 any part of the Bald Eagle delta now preserved was formed, but there is 

 no reason for believing that such land-derived deposits were not forming 

 earlier. Indeed, the character of the Hudson beds shows that such was 

 the case throughout Ordovicic time; that streams coming from the high 

 land of Old Appalachia poured their waters, laden with sand and mud, 

 into the shallow Ordovicic Sea. Such streams could readily bring with 

 them the shed exoskeletons of animals living in their upper reaches and 

 deposit these with the sands and muds on the shallow ocean floor. If this 

 interpretation of the evidence is correct, we should expect to find Ku- 

 rypterid remains throughout the Hudson series, and we should especially 

 look for them in intercalated shales in the Bald Eagle delta and the 

 Oswego sandstone. We feel confident that future discoveries will sub- 

 stantiate this interpretation and will bring to light additional evidence 

 pointing to the river habitat of these organisms. 



Turning now for a moment to the earlier abundant occurrence of 

 Eurypterids in the Belt Terrane, we find that these organisms, if they 

 are Eurypterids, occur alone, without the association of marine organ- 

 isms. Since the beds in which these remains are found are known from 

 other characters to be non-marine in origin, the only rational conclusion 

 that can be arrived at is that these animals were of non-marine habitat. 

 It certainly would be stretching a point to make 1 them marine and have 

 them washed into the area of continental sedimentation, especially as no 

 other marine organisms occur in these strata. 



The isolated occurrences of Eurypterids in marine strata may be ne- 

 glected, since their very isolation makes them of little value in arriving 



