172 H. p. GUSHING PALEOZOIC IN NORTHWESTERN NEW YORK 



State was nearly or entirely submerged for the only time in its geologic 

 history, the early pre-Cambrian possibly excepted. The Lowville lime- 

 stone, while typically developed on the south and west sides of the region, 

 is but thinly developed in the Champlain valley, and is not sharply de- 

 limited from the formations above and below, as in the Mohawk and 

 Black Eiver valleys. 



In the Watertown district the full thickness of the Lowville is shown 

 with a closely related formation (the Pamelia limestone) beneath. This 

 shows considerable thickness only within the Clayton and Tlieresa quad- 

 rangles, and rapidly thins eastward, owing to overlap; so that in the 

 upper Black Elver valley only a thin edge of it is exposed and the over- 

 lying Lowville practically rests on the pre-Cambrian rocks, not only the 

 Pamelia but also the Potsdam and Beekmantown being absent. The 

 Pamelia has entirely disappeared by the time the upper Mohawk region 

 is reached, and there the Lowville rests unconformably on the somewhat 

 eroded surface of the Little Falls dolomite, the local name applied to the 

 supposed Beekmantown of the Mohawk valley. The Lowville here is 

 much thinner than in the Black Eiver valley, and both it and the over- 

 lying Black Eiver limestone are thin and patchy in distribution through 

 the entire length of the valley, owing firstly to unevenness of floor on 

 which they were deposited, and secondly to their representing the extreme 

 northerly edge of their basin of deposit with little subsidence and some 

 local oscillation prevailing along the shore.^' 



The Chazy deposits of the Champlain region were deposited in the 

 restricted Chazy basin, as named by TJlrich and Schuchert, and during 

 most of this period the Mohawk and Black Eiver regions were out of 

 water, as was apparently the larger part of the state; but during the 

 latter part of Chazy time this land area underwent depression, which 

 crept in on the district from the south and west and finally reached the 

 Black Eiver district, as shown by the Pamelia limestone there. This 

 formation is older, biit not greatly older than the overlying Lowville, and 

 its basin of deposit was separated from the Chazy basin by a land barrier 

 of considerable size, of which the whole Mohawk Valley region formed a 

 part, the northerly edge of the Stones Eiver migration on that meridian 

 being buried beneath younger rocks somewhere in southern New York or 

 northern Pennsylvania. The advancing Pamelia shoreline must have 

 had a trend of about north-northwest in northwestern New York, as has 

 already been shown. The Pamelia represents a formation deposited in 

 Chazy time, but in a wholly separate basin. According to TJlrich, there 

 was but scanty deposition in the Chazy basin during Pamelia time. 



"Bulletin no. 95, New York State Museum, pp. 390-391. 



