Page:The Habitat of the Eurypterida.djvu/118

 the littoral belt or the deeper sea; such a fauna finds its counterpart in no waters of normal marine salinity, nor yet in those of modified marine salinity, either estuaries, epi-continental seas, lagoons, or other brackish to fresh water dependencies of the ocean. Thus, though we cannot determine with certainty the place of deposition of the muds from the chemical composition, or from other lithological characteristics, the fauna indicates with absolute certainty that those muds were not deposited in any portion of the sea.

From the foregoing discussion it appears that the Bertie waterlime is best interpreted as a deposit of clastic origin, and that the material was transported by rivers. It also appears that this material could not have been deposited in any part of the sea, for it has not the characters of non-terrigenous deep sea muds, nor the faunal content of a near shore, bay or estuarine deposit. There remains but one place for the deposition of these terrigenous muds and that is upon the land. There seems to be no escape from the conclusion that these lime muds of the Bertie represent the flood-plain or delta deposits from one or more rivers, or else that they accumulated as playa lake deposits. The characteristics of the sediments and faunas of such deposits have been fully described on pages 79-83, and it must be conceded that of all the known modes of deposition the lower flood-plain and upper delta regions of rivers come nearest in their physical and faunal characters to those found in the Bertie waterlime, though, of course, the nature of the sediment demands a source of supply in which calcareous material plays a dominant rôle.

It should be noted in this connection, that shallow water conditions of deposition for the waterlimes of New York and the associated calcilutytes (Manlius, etc.) are indicated by the occurrence of sun-cracked layers at several points. While these have not been found in the Bertie of the Buffalo region, they are wonderfully developed in the waterlimes of the Rosendale-Rondout regions, and in the Manlius of central New York and elsewhere.

Considering the waterlime as a flood-plain deposit, the history during Bertie time would be something like the following:

The early Siluric history of the eastern part of the North American continent had been admirably staged to lead up to the climax of waterlime deposition in many regions during the later Upper Siluric. During the Niagaran there had been a widespread advance of the sea which undoubtedly covered most of southeast and central Canada, as we may judge from the remnants still to be observed in the Lake