Webster on Calton Hill. 233 
re 
The wacke has a greenish grey color, which is pretty uniform. 
The fracture is nearly even and earthy, it is soft, yielding readi- 
ly to the nail, and has a feebly shining streak. A slight stroke 
with the hammer causes the mass to separate in fragments of 
various size, the surfaces of which are often smooth and shining, 
each bed being composed of large distinct concretions, having a 
tendency to the prismatic form. This wacke fuses with difficulty 
before Brooke’s blow-pipe. Specific gravity not determined, as 
it falls to pieces on being moistened. 
The sandstone is for the most part grey, in some parts spot- 
ted red and brown, forming, as the section represents, the last 
stratum seen ; the beds of sandstone are but a few inches in 
thickness, and the last (17) becomes less than an inch ; it is pro- 
ble, however, from the relative situation, from the dip and 
direction, that these strata are a continuation of others seen on 
the other side of the hill, where they are of sufficient thickness 
to have been quarried for the purposes of architecture. The 
beds of all rocks we know vary greatly in different parts, and it 
isnot unusual for them to be some feet at one extremity, grad- 
ually decreasing till less than an inch in thickness at the other, 
or they may even be lost entirely, and gradually regain their 
former size ; and it is not improbable that these beds of sand- 
stone will be found to continue on towards the adjoining hills 
of Salisbury Craig, and Arthur’s Seat, passing under the green- 
Stone and trap tuff. Ea 
The bituminous shale presents the usual characters; inter- 
mixed with it are numerous nodules of the common clay iron- 
stone, the color of which is a yellowish brown, these also fre- 
‘iently present characters common to the three substances, and 
hout the beds, the passage from the one to the other is 
distinct, Whatever may be the opinions in regard to the origin 
of bituminous shale, there can be but one in regard to that of 
Sandstone ; and this has lately received no feeble support from 
the account given us by Dr. Paris, of a formation of this rock 
9 the coast of Cornwall, where, says he, “¢ we actually detect 
‘ature at work, and she does not refuse admittance into her 
Vou..1....No. 3. 4 
