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 have 
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. This 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 Sandlake, 
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 Troy. 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. The 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 the 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 crushed 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 
