GEOLOGY OF 1I1E NORTHERN ADIRONDACK REGION 



399 



1 Dewitt dike near Syracuse. Darton & Kemp, op. cit. p.461, analyst, 

 H. N. Stokes. 



2 Manheim, Herkimer CO., C. H. Smyth, op. cit. p. 325, analyst Smyth. 



3 Manheim, Herkimer co., C. H. Smyth, op. cit. p.2G2, analyst Smyth. 



4 Ithaca, J. F. Kemp, op. cit. p.412, analyst W. H. Morrison ; analy- 

 sis incomplete, and the alumina and magnesia determinations obviously 

 incorrect. 



The first three of these analyses are of fairly fresh material, 

 when the character of the rock is taken into consideration. They 

 suffice to bring out clearly the close relationships of the rocks 

 from the different localities, as evinced by the low silica and 

 alumina and the very high magnesia. While these characters 

 belong to the general rock group to which these rocks pertain, 

 they are the only igneous rocks of the group known in the State, 

 and therefore clearly represent outflows from the same subter- 

 ranean source. So far as known, they are confined to the central 

 part of the State, but the three localities are so widely separated 

 that unquestionably others will be forthcoming. 



ROCK STRUCTURES 



The rocks of the Adirondack region may be separated into three 

 main groups of widely separated age, owing to the fact that there 

 have been three main periods of rock formation in the region, 

 separated by protracted intervals of wear. The Precambric 

 rocks constitute the first group, the early paleozoics the second, 

 and the pleistocene deposits the third. The last are so recent 

 as to be in substantially the condition in which they were depos- 

 ited, unconsolidated masses of glacial deposits and of marine 

 and fresh-water sands and clays. A vast time interval separates 

 them from the paleozoics, which are all thoroughly indurated 

 rocks, but which are otherwise not greatly altered from their 

 original condition, though they have suffered somewhat from 

 earth stresses and movements. Another vast time interval sepa- 

 rates these from the Precambric rocks, and the latter under- 

 went profound changes in character during this interval. They 

 therefore present structural features which are confined to them, 

 as well as others which they share with the Paleozoic rocks. 



Foliation 



In the Adirondack region the Precambric rocks alone have 

 suffered metamorphism, but they are so profoundly metamor- 

 phosed, the late dikes always excepted, as to have been vastly 



