NEW YORK STATE MUSEUM 



Helderberg regions. There are, however, good instances of the 

 formation of such inliers, still going on, seen in the islands of our 

 large fresh-water lakes, especially in Lake Champlain, where the 

 islands composed of Paleozoic rocks are being surrounded and grad- 

 ually buried by the deep alluvial deposits filling up the lake. This 

 is for instance well shown in the case of Valcour island, near 

 the mouth of Ausable river whidh is rapidly pushing a delta into 

 the lake. 



Another group of depositional inliers, however, is well repre- 

 sented in this State. The best instances of this are the numerous 

 hummocks of Grenville and other Precambric rocks protruding 



through the Potsdam sandstone on 

 the north and especially on the 

 northwest side of the Adirondacks. 

 These are especially- well seen in 

 the region south of Alexandria 

 bay [sec fig. I, 2]. They orig- 

 inated from the irregular surface 

 of the Precambric floor result- 

 ing from the differing hardness 

 of the rocks. The mostly small, 

 elongate hills emerge now from 

 beds of Potsdam sandstone which 

 by their position and the coarser 

 texture of their basal portions, 

 clearly show deposition upon and against these hills. The latter 

 were not true outliers in Potsdam time, since their strata were 

 still in connection with the Adirondack mass, but they have 



Inliers of Pre cambric rocks 



/\ s\ s\ 



\ /\ /\ ✓ in Potsdam sandstone 



near Alexandria, N. Y 

 1 in. 



Scale 1 5 m. = 



Fig. 2 Diagrammatic section of Precambric inliers near Alexandria, N. Y, 

 I Precambric 



s\ y\ /\ 

 ^ A /\ / 



Potsdam sandstone 



become true inliers in the Potsdam formation because exposed 

 again through the agency of erosion. It is then illogical to term 

 these outcrops outliers as is generally done, since they do 

 not fulfil the conditions of an outlier which according to the cur- 

 rent conception is a detached mass of rock, resting upon and sur- 

 rounded on all sides by older rocks. These supposed outliers are 

 only " detached " on the surface, but still connected with the 



