Smyth — Crystalline Rocks of St. Lawrence County. 483 



distance from, the large belts, and range from less than a mile to several 

 square miles in area. There is nothing to distinguish them from the larger 

 belts except their limited dimensions, and they must be regarded as 

 constituting a portion of the limestone series. 



As to the character of the limestone in the various areas, it is scarcely 

 necessary to speak here, descriptions having already been given in the papers 

 above cited.* It is always highly crystalline, ranges in color from white to 

 dark bluish grey, and often contains disseminated and aggregated silicates. 

 Of these, the most important are serpentine, forming ophicalcite, and 

 tremolite. The latter renders the rock more resistant to weathering, and 

 sometimes is so abundant as to constitute a tremolite schist. The limestone 

 contains a variety of gneissoid rocks, some of which are doubtless interbedded, 

 while others are probably altered intrusives. These gneisses often show 

 a great amount of contortion and crushing, as a result of the application of 

 inteuse pressure. The limestone itself, on the other hand, presents a massive 

 undisturbed appearance, with no indication of its subjection to pressure 

 beyond the development of poly synthetic twinning — iR. Owing to the 

 difference in the nature of the rocks they have been affected very differently 

 by pressure, the gneiss having yielded by folding and fracture, the limestone 

 by flow. It is quite possible, however, that a considerable amount of 

 fracturing actually occurred in the limestone, but this has been obliterated by 

 subsequent recrystallizath >n. 



In considering the small patches of limestone, a point which should not 

 be overlooked is that, owing to the easy weathering of the rock, outcrops are 

 more generally wanting than in the case of the surrounding resistant gneiss. 

 For this reason, the real extent of these areas is probably often greater than 

 it appears, while there are, doubtless, many such patches that have been 

 entirely overlooked. 



When the distribution of the limestones is viewed in a broad w ay, it 

 becomes apparent that these rocks have their greatest development in the north- 

 western part of the region, decreasing as the eastern and southern parts of the 

 county are approached. In the former district lie all of the extensive belts, 

 while in the latter only scattered patches of limestone occur, gneiss being the 

 prevailing rock. This relation is very marked and is probably persistent 

 throughout this portion of the Adirondack region. There can be little doubt 

 that the combined Macomb and Gouverneur belts constitute the most extensive 

 area of crystalline limestone, and that the rock decreases rapidly in passing 



• Op, ctt. ; also, Transactions New York Academy of Sciences. XII., pp. H7-108 and ','03-217. 



