346 



NEW YORK STATE MUSEUM 



the shores of Upper Chateaugay lake may be mentioned as 

 localities where they are exceedingly numerous. Followed to 

 the south and west, they rapidly diminish in number and become 

 rare or wholly absent. Thus Kemp reports many from Essex 

 county, mainly in the north, but very few from Washington and 

 Warren. Franklin county is much larger and with a propor- 

 tionate much greater area of Precambric rocks than Clinton, 

 yet only some forty of these dikes have been discovered there, 

 and these mainly in the eastern portion. Though many more 

 doubtless remain undiscovered, the relative abundance can be 

 calculated, and they are six to eight times as abundant in Clin- 

 ton as in Franklin. In St Lawrence, Hamilton and Herkimer 

 counties they are practically absent, and the few known are 

 toward the northeast. Smyth reports them in comparative 

 abundance in the Thousand islands region on the west border 

 of the district, and a single large dike of diabase is found in 

 the Little Falls outlier on the far south. So far as the present 

 Adirondack region is concerned, the igneous activity of this 

 time centered in Clinton county, dying out toward the south 

 and west. As to the extension northward and eastward, noth- 

 ing can be stated, since the Precambric rocks pass under a 

 paleozoic cover in those directions. Diabase dikes are however 

 fairly abundant in Canada in the region beyond this cover. 



The centering of the activity in Clinton county becomes the 

 more apparent when the distribution of the two varieties of the 

 dikes is taken into consideration, the red, syenite dikes being 

 practically confined to that county. They are far less num- 

 erous and of much more restricted distribution than the dia- 

 bases. Only 26 dikes of this class have been noted, of which 

 19 are on Rand hill, where exposures are numerous and detailed 

 work has been done. No doubt there are many others elsewhere, 

 but it seems quite certain that they are practically confined to 

 the county, only one having been noted outside its limits, and 

 that in Franklin not far from the boundary. Even on Rand 

 hill the diabases much outnumber them. The display of dikes 

 there is the most impressive known in the Adirondack region. 

 If any volcanos were built at the time, surely the roots of one 

 gigantic one are here. 



As has already been stated, these rocks are found at the present 



