246 J. F. KEMP — ROCKS OF THE EASTERN ADIRONDACKS. 



reous sediments, heavily metamorphosed. As to the larger areas, the 

 writer cannot accept Dr Hunt's view that the Port Henry exposure is a 

 veinstone, but of the nature of the accompanying hornblendic and 

 pyroxenic schists it is impossible to feel so certain. They shove close 

 analogies with metamorphosed gabbros, and gabbros may even be traced 

 from massive facies into schistose forms, practically identical with them, 

 yet their wide distribution, always along with the limestones, presents an 

 extraordinary invariability on both sides of the mountains. There are 

 also not a few veins whose mineralogy approaches that of the larger 

 limestone areas, but whose long and narrow character in the midst of 

 anorthosite walls indicates that they are undoubtedly vein-fillings. 



The Limestones of Essex County. 

 location, extent, relations and mineral constituents. 



In Essex county the limestone areas of largest size are in Crown Point, 

 Ticonderoga and Newcomb townships and are each several square miles 

 in extent. Moriah and Keene townships have also large and well exposed 

 outcrops, and in addition small lenses up to 50 feet thick and a few hun- 

 dred feet long are not uncommon in Schroon township, associated with 

 black hornblendic schists, which often cover a much greater area than 

 the limestone, and which are so characteristic that we have come to rec- 

 ognize them as an indication of the series. 



Split rock, the peculiar little promontory in Essex, is limestone with 

 numerous included knobs and beds of silicates. 



In the southwestern part of Chesterfield township ten or twelve miles 

 from Keeseville there is a notable outcrop of the serpentinous variety 

 which has been somewhat quarried. 



In southern Jay township there is a good sized ledge, and in Lewis 

 there are not lacking small outcrops. 



The accompanying map (see figure 1) makes it evident that these 

 rocks occur over nearly the whole county in small exposures. 



Oftentimes, as already stated, the black garnetiferous schists, so abun- 

 dantly associated with them, alone are seen and serve to indicate their 

 foruier presence. 



The white limestone is coarsely crystalline, usually graphitic, and 

 often set with little scales of phlogopite. It is frequently charged with 

 coccolite or yields specimens practically consisting of this mineral. 

 Seams of quartz are not lacking, and in one or two cases considerable 

 amounts of pure silica have been mined. Rose quartz is characteristic- 

 ally common. Tht exposures never consist of pure limestone for any 

 extended thickness. In the larger areas great bunches of various sili- 



