364 GEOLOGY OF THE SECOND DISTRICT. 



undoubtedly continuous ; but at the present time, we find it only in separated beds : frequently 

 the inferior beds remain, but more generally the upper are entirely removed. 



Superficial Covering, Drift, or Boulder System of St. Lawrence. 



The Boulder system or drift of this county differs in no respect from that of Franklin. It 

 is, however, more favorably located for observation, as St. Lawrence has a larger territory 

 than Franklin, and lies in a direction well formed to receive the floating materials from the 

 north. The country slopes generally to the St. Lawrence river, in no part of the county steeply, 

 but in by far the greater part very gradually. 



The towns on the river, those which are underlaid by the calciferous sandrock, are low. 

 Passing east from this to the sandstone of Potsdam, we ascend as it were from a lower ter- 

 race to a higher ; and in going still farther east, from the potsdam sandstone to the primary, 

 wc reach a higher terrace still, and a portion of the county which is thrown more into hills 

 and ridges ; but still even in this part, for a wide space, there are but few steep and abrupt 

 eminences. Upon all tliese terraces we find a thick mantle of sand, gravel and boulders, all 

 of which belong to one era, or one system : it is the Drift or Boulder system. Now although 

 the river towns arc lower and more level, still they do not present a greater accumulation of 

 these loose materials than the higher towns, and perhaps even not so great. This is contrary 

 to what we should expect. The materials in the former or lower district, however, are all 

 finer ; that is, there is more sand and gravel, and it is spread more evenly over the surface. 

 But there is a difference in another respect : there is more clay, which is frequently laid bare ; 

 and the loose materials, instead of having accumulated, have been apparently removed. Upon 

 the sandstone region, the drift begins to accumulate, and we now find quite thick and heavy 

 beds, and coarser too than in the limestone district. At the next step east, which brings us on to 

 tlie primary, we begin to meet with large boulders imbedded in coarse gravel and sand. These 

 beds lie in steep hills or ridges. In this arrangement, we find that it forms no exception to other 

 parts of the district ; for without exception, I believe, the coarse heavy materials have been trans- 

 ported to the higher levels, where they form stony rough ridges. The kind of boulders which 

 prevail are those of granite and sandstone ; the former arc the transported rocks, and the latter 

 appear to have been broken from the rock below. Tliey are less rounded than the granite. 



In the primary class we find also a few large boulders of hypersthene rock, particularly in 

 the neighborhood of Ogdensburgh : generally they are not carried so far from the river as those 

 of granite. These boulders may be traced northwards ; they do not, therefore, appear to have 

 been derived from the hypersthene rock of Essex ; for we do not find that they increase in 

 that direction, but rather diminish. We, however, find them continuously in a line parallel 

 with the river : it appears, therefore, that thcv came from that direction. 



Comparing the northeast part of the county with the southwest, another difference is found 

 to prevail. In the towns in the former direction, a great many boulders of limestone are 

 found, some of which belong to the rock of the county : they are of the calciferous, but 



