6 Report of the State Geologist. 



character and in resistance to erosion that the boundary is not especially tor- 

 tuous, and though it is quite possible that isolated patches of the Potsdam 

 may occur within the gneissic area, as has been found to be the case in Essex 

 and Clinton counties, their discovery would require the mapping of a much 

 larger area. 



Westward from Parishville, the Pre-cambrian rocks at the boundary con- 

 sist of an entirely different series of gneisses with belts of crystalline limestqne. 

 i. 



These rocks resist erosion very unequally, and as a whole are less resistant 

 than those along the boundary to the eastward. The change in the topogra- 

 phy, which is there strongly marked, is here much less serviceable. Further- 

 more these rocks were profoundly and unequally eroded in pre-Potsd&m time. 

 In the troughs thus formed the Potsdam sandstone was deposited and is yet 

 found in them far within the area occupied by the older rocks.* To fix 

 accurately the limits of the formations here will require areal mapping over an 

 extended territory. 



No rock of younger age than the Calciferous was found in the district 

 examined, the Pleistocene deposits of course excepted. Outcrops occur so 

 seldom that it is useless to attempt to show the limits of the formation 

 except in the most general way. 



On the map accompanying this report these boundaries are indicated, and 

 the various outcrops seen are located. It must be borne in mind that the 

 small scale of the map makes the outcrops appear much more numerous than 

 is really the case. 



TOPOGKAPHY. 



In a broad sense the topography of the district under consideration is 

 simple. The Pre-cambrian rocks come to the boundary in a succession of low 

 ridges and knobs which ordinarily do not protrude very greatly above the 

 general level, and which are separated by shallow, drift-filled depressions. 

 Thence northward the country is heavily mantled with drift, has little relief, 

 and slopes away to the north and north-west toward the St. Lawrence valley. 

 Only rarely does the underlying rock project above the drift, the small 

 streams do not cut through it, and in general the only outcrops to be seen are 

 those exposed in the larger streams where they are out of their pre-glacial 

 channels. 



The minor features of relief which characterize districts of morainic drift 

 (and much of it here is morainic) are here obliterated over much of the district, 

 more especially along the stream valleys, by the deposits of sand laid down 



* By way of illustration see Smyth's map of the vicinity of Gouverneur. Rep. N. Y. State Geol., 1893, Vol. I, p. 498. 



