94 THE HABITAT OF THE EURYPTERIDA 



origin, though Walcott insists that they belong to this group. Clarke 

 and Ruedemann hold, however, that the specimens from the Altyn 

 limestone of Alberta are undoubtedly merostomes, but they ques- 

 tion the correlation of the Altyn and Belt Terrane, and the conse- 

 quent reference of the remains from the two formations to Beltina 

 danai. (This has been discussed on pp. n-13.) The Belt Terrane 

 material, nevertheless, has a very strong resemblance to the euryp- 

 terid fragments from other horizons, though the specimens all lack 

 the surface markings characteristic of the eurypterids. Some of the 

 most typical material is figured on plate 25 in the Bulletin of the 

 Geological Society of America, Vol. X, 1898, and again in the Smith- 

 sonian Miscellaneous Collections, Vol. LXIV, No. 2, plate 22. 



Of the conditions of sedimentation prevailing during this period 

 Walcott says: 



"Briefly summarized, the Algonkian period in North America 

 with its great epicontinental formations was a time of continental 

 elevation and largely terrigenous sedimentation in non-marine bodies 

 of water, and of deposition by aerial and stream processes in favorable 

 areas 



"The North American continent was larger at the close of Algon- 

 kian time than at any subsequent period other than possibly at the 

 end of the Cretaceous, when the land was equally extensive. Indeed, 

 it is highly probable that its area was greater then than even now, for 

 no marine deposits of Algonkian age containing pre-Cambrian life, 

 as they were laid down in Lipalian 1 time immediately preceding the 

 Cambrian period have been discovered on the North American con- 

 tinent or elsewhere, so far as known" (290, 81, 82). 



Walcott does not wholly subscribe to the fresh water habitat of 

 these eurypterids early for he speaks of Beltina danai as "possibly 

 of marine derivation" and uses the presence of this fossi] in the Belt 

 Terrane as an indication that a connection of the Cordilleran geo- 

 syncline with the sea was temporarily effected allowing "at least a 

 crustacean, and a few annelids" to become adapted to the Montana- 

 Alberta sea. It is clear that Walcott allows this entrance of the sea 

 into the Beltian lake only in order to account for the presence of the 

 eurypterids and annelids and to conform to the prevailing opinion 

 that the early eurypterids were marine organisms. This concession 



1 Lipalian is a term proposed by Walcott in 1899 "for the era of unknown marine sedimentation 

 between the adjustment of pelagic life to littoral conditions and the appearance of the Lower Cam- 

 brian fauna. It represents the period between the formation of the Algonkian continents and the 

 earliest encroachment of the Lower Cambrian sea" (290, 82). 



