NAPLES FAUNA IN WESTERN NEW YORK, PART 2 205 



following the line of the Mohawk river and the southern shore coming in 

 from the southwest along the inner margin of the Appalachian ridges, the 

 two meeting in a narrow curve which gave to this inward projection of the 

 sea but relatively slight breadth. A shoaling of the water at this end of 

 the gulf, a differential movement raising the crust in this region, com- 

 menced when Portage time was well under way, and produced banks 

 which must have become a more or less efficient land barrier, throwing the 

 interior coast line well to the west, and for a while, probably for the 

 remainder of Portage time and perhaps through all the subsequent epoch, 

 excluded forms of marine life from these almost landlocked waters. This 

 was the place and such the origin of the Oneonta sands, a mass of 

 strata freely tinted with red and green. At the head of the gulf, where the 

 waters were earliest affected by the barrier, these lie close on the very basal 

 layers of the marine contemporaneous Portage sediments and rise ever 

 higher in the section as they encroach southward on the gulf by the out- 

 ward extension of the barriers. Having become shut off from free access 

 to the salt water by land bars over which the sea entered only at times of 

 stress or when the barrier was parted for a while, this apical or Albany 

 segment of the gulf was gradually purified by heavy land drainage and 

 became a large brackish or fresh-water lagoon in which no true marine 

 organisms could flourish. 



Lake Oneonta. The history of this Devonic lagoon may be outlined 

 thus. Beginning almost directly after the close of Hamilton time, the 

 marine waters were shut out of the Albany end of the Appalachian gulf in 

 such manner as seems to indicate the establishment of estuarine conditions 

 at the head of the gulf. With progress of Portage time this lagoon 

 expanded in area, spreading to the*west across the present Chenango valley 

 and to the south into Pennsylvania. During the latter part of Portage 

 time this body of water was so nearly purified of its salinity as to support in 

 abundance a bivalve, Archanodon or Amnigenia catskillensis, 

 very like the fresh-water Unios of the present, and doubtless of similar habit 1 



'Clarke. N. Y. State Mus. Bui. 49. 1901. p. 199. 



