A PART OF THE TACONIC SERIES. 



89 



In tliis vicinity, we have the lower Helderberg rocks, in addition to the Chainplain 

 group, reposing upon the Taconic system. The occasional appearance, then, of rocks of 

 another age, under the circumstances and conditions presented at Chatham and Hudson 

 and the intervening country, throws an obscvirity over the questions of age, identity, etc., 

 which rarely calls for solution in other places. Nevertheless the evidence is so strong in 

 favor of the interpretation I have given of the relation of these masses, that I have had 

 no doubt of its propriety ; although when I published my Report of the Second Geological 

 District, I was not prepared with proofs to sustain it. 



Turning the attention of the reader once more to Washington county, he will find a 

 few interesting examples in the relative position of the members of the two systems : the 

 calciferous of the New- York system, and the black slate and coarse taconic slate of the 

 Taconic system. The first example is an illustration of the rocks of Bald mountain. This 

 knob is one of the highest points that skut the valley of the Hudson upon the east. It 

 overlooks the valley for a great distance ; and from it, also, the interior mountains of the 

 northern wilderness at the sources of the Hudson loom up in a bold outline in the north- 

 western horizon. Passing over, however, the magnificent scenery of this spot, I proceed 

 to speak of the structure of the mountain. The diagram fig. 11 will aid in explaining the 



most important parts. 



* 



Tig. H. 



The slope a, b, c, d, looks to the west. The calciferous sandstone is represented by d, d. c, indicates the blue 

 portion of the calciferous sandstone I have had occasion to speak of in other places : it forms the purest lime, 

 though it is of a much darker color than that represented at d. The taconic or rather black slate appears at b, b, 

 b, b. Upon the borders of c, c, is a singular dark-brown close-grained sandstone. From these facts, it appears 

 that there must be a double fracture, by which the black slate is exposed at b, b. The limestone of the upper 

 part of the mountain is thin-bedded, and alternates with a calcareous slate ; the lower mass d, is more in keeping 

 with the common calciferous sandstone. A very curious intrusion of fragile greenish slate occurs just above c, 

 represented by the perpendicular line ; it is two feet thick, in vertical smooth walls like a dyke. As it truly is 

 a slate with vertical laminae, it is really perplexing to account for its pesition and formation under such singular 

 relations. The base of the mountain a, b, is upon the right, where a hundred yards of the slate is exposed in a 

 continuous line : it is overlaid here by thick beds of tertiary clay, a, a. 



[Agricultural Report.] 



12 



