﻿122 NEW YORK STATE MUSEUM 



Paleozoic altitude and climate 



During the Lower Siluric the immediate region was from time 

 to time submerged, at other times was above sea level. During 

 submergence there were neighboring lands. It is apparent that all 

 were of low altitude. During emergence there was but trifling wear 

 on the exposed land surface. During submergence the adjacent, 

 lands furnished but little land wash, though the Precambric rocks 

 of which they were formed were capable of supplying great quanti- 

 ties of sand and mud under conditions of any freedom of drainage ; 

 and they were near at hand and of much extent. A small thickness 

 of sand marks the horizon of the Pamelia-Lowville break, other- 

 wise the formations are unbroken limestone, until the shales of the 

 upper division come in; and these are more indicative of stronger 

 currents in the marine waters, than of especially increased altitudes 

 of the neighboring lands. The succeeding Oswego sandstone seems 

 a continental, rather than a marine deposit and indicates freer 

 drainage and somewhat greater altitude. 



But little has been gleaned from the region itself as to climatic 

 oscillations in these early times. The upper Pamelia was marked 

 by a somewhat arid, and perhaps warm climate, as has been seen. 

 Probably the same was true of the Oswego-Medina, though that lies 

 outside our district. The Potsdam climate is a puzzle. Farther 

 east, where the basal Potsdam consists largely of arkose, and where 

 the Precambric underneath shows the same freshness and the same 

 irregularity of surface under the Potsdam that it does here, we 

 have expressed the opinion that the sandstone was a continental de- 

 posit, so far as the basal portion is concerned, and that the climate 

 was arid. Here however, with the same character of floor, we have 

 a pure sand deposit, instead of arkose. The unweathered character 

 of the Precambric rocks, the absence of residual weathered material, 

 except in very scanty amount in the most sheltered situations, 

 and the general base-leveled character of the surface, seem to 

 point to long continued wear under conditions of aridity and 

 removal of disintegrated material by the wind. Under those 

 circumstances however the residual products should be arkose, in- 

 stead of pure quartz sand such as constitutes the Potsdam here. 

 There is much more feldspar in the basal Pamelia sand than in 

 the Potsdam, and even in that it is not in great quantity. We are 

 unable to correlate this quartz sand with conditions of climatic arid- 

 ity, and equally unable to explain the character of the Precambric 

 surface, and the unweathered condition of the rocks, satisfactorily 

 to ourselves, on any other basis. 



