WITH THE PRIMARY SYSTEM. 59 



worn down, leaving the range of knobs as we now find. Thus Bald mountain and Mount 

 Toby, with several others in the neighborhood, stand in insulated high points, capped with 

 the Calciferous sandstone; while at their bases the Taconic slate appears in an outcrop, 

 varying in thickness from fifty to two hundred feet. But the Calciferous sandstone is not 

 confined to the line in the immediate borders of the valley of the Hudson: it is found in 

 patches twenty rules east, reposing as at the west upon the slates; probably, however, 

 upon the magnesian slates. 



From these few remarks upon this rock, its position and relations will be understood. It 

 is the lowest member of the New-York system, as well as the most easterly; and occupy- 

 ing an exceedingly long range, it is not surprising that its lithological character should be 

 found diverse and continually changing. 



I have now exhibited the actual relations of one of the Taconic rocks to the New- York 

 system ; that member which on all hands has been considered as the nearest related to the 

 Hudson river shales and sandstones, or the one which approaches the nearest in litho- 

 logical structure and condition to these rocks. 



Having demonstrated the relations of the most westerly mass, and having shown that it 

 is not only unconformable to the New- York rocks, but inferior to them, I proceed to speak 

 of the relations of the most easterly members of the Taconic with the Primary system, for 

 the purpose of showing that the Taconic system is the newer of the two, or that it holds an 

 intermediate position between the Primary schists and the New-York system. 



At several localities which I have often examined in Vermont and Massachusetts, the 

 most easterly rock is the Brown sandstone, or Granular quartz. A fine exposure exists at 

 Sunderland (Vermont) , nearly east of Salem in Washington county (New- York) ; or 

 rather of Miller's falls, on the Hudson river. The quartz succeeds a magnesian slate, 

 with which it is conformable ; and on being traced to the primary schists, is found to 

 repose upon them unconformable, the former ranging N. 20° E. and dipping at an angle 

 not exceeding 10°, while the primary schists have a much steeper dip to the east. The 

 precise line or plane of junction is concealed by drift, but I was able to observe it within 

 a few yards. Near the junction, the slaty quartz is charged with crystals of schorl and 

 octahedral iron. There are also beds of what may be termed porphyritic quartz, since they 

 contain crystals of felspar. A portion of the lowest mass, however, is a breccia, as in many 

 other important localities, of which I shall have occasion to speak hereafter. The quartz, 

 as is frequently the case, is interlaminated with a siliceous slate, by which its stratification 

 is very clearly shown, giving us the means of distinguishing the planes of deposition from 

 the very strong natural joints and those of cleavage. 



