98 THE HABITAT OF THE EURYPTERIDA 



siliceous sediments could come, and the characteristics of the sedi- 

 ments just noted clearly point to that continent as the source. 



It will probably be readily accepted that the Normanskill and 

 Schenectady are of terrigenous origin, especially since they are several 

 thousand feet thick, but the point which is difficult of determination, 

 is the origin of the fauna of these formations. That the sediments 

 were fluviatile does not at all imply that the organisms in those sedi- 

 ments were also fluviatile. Indeed, it is usually argued that the 

 presence of graptolites and "sea- weeds" in the same beds with the 

 eurypterids is ample proof that all these types of life were marine 

 and that they lived in the littoral zone in the sandy and muddy facies. 

 First, in regard to the " sea-weed" Sphenophycus latifolius, there is 

 no reason that I know of why such plant remains could not have been 

 washed in from the land or might not have been living in the rivers, 

 and have thus been swept into the sea. Secondly, it is evident that 

 the presence of graptolites does not indicate deep sea conditions of 

 quiet sedimentation as so often stated. Certainly, there is nothing 

 incompatible with the assumption that the graptolites were spread 

 out on mud flats, or river flood-plains as modern hydroids are, when 

 washed in by the sea. At least the possibility must be granted that 

 the pelagic graptolites would after death be more likely to float near 

 or on the surface of the water until thoroughly decayed and disinte- 

 grated, rather than sink to the bottom, and be buried by sediments. 

 In such a case, their only chance for preservation would be through 

 stranding upon some surface where they could be quickly entombed 

 by layers of mud or sand. This line of argument has only just been 

 propounded by Professor Grabau, and while heretical it yet explains 

 many curious occurrences. 3 Thus, although no definite statement 

 can be made at present regarding the precise habitat of the grapto- 

 lites, we may consider that it is reasonable to assume that their re- 

 mains are chiefly found in formations accumulating near land espe- 

 cially on delta surfaces. If the graptolite-bearing beds are thin we 

 may suppose that they were formed by frequent inundations from the 

 sea, but when 1500 feet thick, as is the case of the Schene'ctady beds 

 throughout the entire thickness of which graptolites occur at intervals, 

 then the only interpretation is that the beds were a series of flood- 

 plain and delta deposits, mostly above sea-level, and that the grapto- 

 lites were stranded on the low-lying land areas by periodic incursions 



s Professor Grabau has discussed this subject very fully in his lectures, with especial reference to 

 the Graptolite beds of Europe. He expects to publish soon on this subject. 



