GEOLOGY AND PALEONTOLOGY OF THE SCHOHARIE VALLEY 233 



this sea a few migrants were added to the fauna which had 

 developed from the Onondaga fauna; other migrants continued 

 to arrive from the seas covering South America, by way of the 

 Indiana passage, while European arrivals continued to enter the 

 sea through the Connecticut channel.^ Whatever the value of 

 the eastern channel may have been during Onondaga time, its 

 efficiency as a transmitter of foreign invaders was greatly 

 diminished during Hamilton time, and before the end of that 

 period ceased entirely. This will be realized when the nature 

 of the Hamilton sediment in the northeastern portion of the 

 Mississippian sea is considered, for it indicates conditions 

 which would hardly admit of the introduction of any except the 

 most hardy shallow water types from that quarter. 



At the beginning of Portage time, Laurentia, the northern 

 continent, and Appalachia, the southeastern continent, were 

 again united. 



The apex of the Appalachian gulf during the earlier part of 

 Portage time, must have reached to Albany, the northern shore 

 approximately following the line of the Mohawk river and the 

 southern shore coming in from the southwest along the inner 

 margins of the Appalachian ridges, the two meeting in a narrow 

 curve which gave to this inward projection of the sea but rela- 

 tively slight breadth. A shoaling of the w^ater 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. At the head 

 of the gulf, where the waters were earliest affected by the bar- 

 rier, these lie close on the very basal layers of the marine con- 

 temporaneous Portage sediments and rise ever higher in the 

 section as they encroach southward on the gulf by the outward 

 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 



^Schuchert Am. Geol. 32:162. 



