24 Geology and Mineralogy of a part of Massachusetts, &c. 
elements is continually breaking down the larger rocks 
through these seams. 
‘Rubble Stone is more abundant some distance from the 
river, and generally lies on more elevated ground. The 
mountains in Grafton are composed of it, and it is found on 
the summits of others. | 
Near the city of Troy, the gray wacke corresponds more 
perfectly with the European descriptions of this rock. It 
contains, with the materials before mentioned, fragments of 
argillaceous slate, siliceous slate, and lime stone, and has a 
partially slaty structure. 
The extent of the gray wacke in the southern part of the 
section, has not been satisfactorily ascertained. I believe, 
however, it becomes less abundant in this quarter on the 
east side of the Hudson. 
Though separated from this stratum of gray wacke by a 
range of hills, the lowest parts of which are several hundred 
feet above the valley of the Housatonick, masses of rub- 
ble stone, and sometimes of the common gray wacke, are 
found in Berkshire county. I have seen them from the 
weight of a few pounds to that of several hundreds and 
sometimes tons ir weight, in Pittsfield, Stockbridge, and 
Sheffield. They are found also in Williamstown; and 
some have lately been found by Dr. Emmons, high as the 
range of mica-slate, in Chester. ‘They are always rounded 
masses, and so exactly like the gray wacke of this stratum, 
that one cannot fail to believe that they have been trans- 
ported by the agency of water from this, their original 
place. 
Gray wacke contains organic remains. On the west 
side of the Hudson, at Newburgh, Cattskill, &c. they are 
abundant in this rock. Some specimens seem to be compo-_ 
sed chiefly of terebratulites. In the gray wacke in this 
section, I believe they have not yet been discovered. It is 
probable, however, that they will yet be discovered in the 
neighbourhood of Hudson, since they are found at a short 
distance on the other side of the river. I have a mass of 
petrified shells, which were picked up at a small stream in 
Nassau. This place is in the region of gray wacke. But it 
is impossible to ascertain the geologica! relations of these 
shells, so completely are they detached from the rock which 
contained them. As they effervesce with acids, they proba- 
bly belonged to the shell limestone. 
