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 question the correlation of the Altyn and Belt Terrane, and the consequent reference of the remains from the two formations to Beltina danai. (This has been discussed on pp. 11-13.) The Belt Terrane material, nevertheless, has a very strong resemblance to the eurypterid 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 Smithsonian 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 terrigerious 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 Algonkian 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 continent 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 fossil in the Belt Terrane as an indication that a connection of the Cordilleran geosyncline 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
- ↑ 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 Cambrian fauna. It represents the period between the formation of the Algonkian continents and the earliest encroachment of the Lower Cambrian sea" (290, 82).
