ROOFING SLATE. 71 



The members subordinate to the Taconic slate have been enumerated. The order in 

 which they are disposed is exhibited in the plate of sections. In three of them only Iiavc 

 fossils been found. The coarse slaty sandstone of a greenish color, which is the first mass 

 met with going from west to east, is the mass in which the fossil represented fig. 10 was 

 found. 



Not far distant is a bed of sparry limestone, more slaty than the rock described under 

 that name. Tliis is only about fifteen feet thick. The question comes up, whether this 

 mass may not be the thin western edge of the true sparry limestone, the rock next 

 described? I know of no facts which favor this view, except the very equivocal one, 

 lithological character. 



Another mass whose characters are quite remarkable, is a breccia lying at the western 

 base of the Taconic range. It is developed largely ; more so, I believe, in East Sandlakc, 

 and about twelve miles east of the Hudson at Albany. It forms a high broken rough 

 range of hills which terminate just south of the macadam road in Pittstown, sixteen miles 

 west of Tro}\ There are no rounded pebbles in the rock, but angular ones nearly half 

 an inch in diameter. Much of the rock resembles a porphyry ; it is thick-bedded, and 

 interlaminated with fine green slate. Tiie thickness of the mass remains undetermined : 

 it is probably two hundred feet. Some portions of this mass have a very strong resemblance 

 to the thick-bedded sandstone of the Champlain group. 



ROOFING SLATE. 



This is one of the most easterly of the subordinate masses. It is a fine bluish black 

 slate, even-bedded, and well adapted for roofing. Some of the layers are slightly pyri- 

 tous. Geologically it is interesting, from the great abundance of marine vegetables. 

 Plate XVII. fig. 1, is copied from a lamina of slate from the Hoosic quarry, about twenty 

 miles east of Troy. This quarry has been wrought over twenty years, and no other fossil 

 has been discovered. The absence of the mollusca here, too, is well worthy of notice. 

 It is possible that two species of fossil vegetables may exist in this slate ; one with a narrow 

 frond, and the other with a wide one. 



RANGE AND EXTENT OF THE BLACK AND TACONIC SLATES. 



The black slate is not as well exposed as tlie taconic ; there is, therefore, some uncer- 

 tainty in regard to it. It is the rock adjacent to the Champlain and Hudson valleys, and 

 more frequently that which we observe immediately beneath the calciferous sandrock, or 

 cropping out from beneath it. What we see of it, is frequently in a cruslied condition, 

 and bounding the taconic slate on the west in New-York and Vermont. I have not recog- 

 nized it about Albany or Troy. Greenwich in Washington county is the most southern 

 point at which I have observed it. It extends north as far as St. Albans in Vermont. I 



