Fluctuations in Level of the Quartziies. 137 



In the figure the conglomerate is represented as joining the 

 quartzite on a shelf or terrace such as is often formed by the 

 breakers on a rocky coast. This was observed to be true in 

 some cases, but may not be a general fact, though I suspect it is. 



5. Following the period of the formation of the conglomer- 

 ate, which previous investigations have identified as the Mid- 

 dle Potsdam, there occurred another subsidence indicated by 

 the formation of the sandstone marked dd, Fig. 2. This sub- 

 sidence seems to have continued until the entire formation was 

 submerged beneath the ocean level, and buried beneath its 

 sediment. This, however, I ami not able to positively demon- 

 strate in respect to certain portions of the south range. East 

 of the Lower Narrows, resting upon and rising high above the 

 north range, is a high bluflP, which presented at a distance the 

 appearance of sandstone, and which I was assured by Mr. 

 Canfield it was. The elevation of this seemed about equal to 

 that of the higher portions of the south range, but I had no 

 means of measurement. Even should its elevation be found 

 to be considerably less, its approximation to the height of the 

 quartzite can scarcely be regarded as less than a demonstration 

 of the fact in question, when it is remembered that at least 

 400 or 500 feet of sandstone in the vicinity have been swept 

 away by eroding agencies, and that this bluff" must have suf- 

 fered much more denudation proportionally than the quartzite. 

 I conjecture, however, that the quartzite rose into the horizon 

 of the lower magnesian limestone. 



On the high bluff just east of the lake, in excavating for a 

 cistern, Trenton fossils in a siiicified condition were thrown 

 out. This portion of the bluff" does not. seem to have been 

 visited by the glacial agencies, although northern drift occurs 

 a short distance east. This will not seem strange when it is 

 known that the drift, even on the lower lands, extends but a 

 short distance west of this. There was no foreign drift dis- 

 cernable in the material excavated or in the vicinity, and the 

 quartzite bottom did not indicate glacial erosion. These facts 

 10 



