334 ON THE ANCIENT GRAUWACKE 
cies, occurring in the lower part of the Upper Silurian division. 
Sir Roderick adds, as further remarkable, that on submitting to 
the Continental geologist some of the shales and nodules in 
which these Ayrshire shells are imbedded, “he declared to 
him that he might produce our Scottish rocks as Bohemian 
specimens.” The Bohemian species of orthoceratite has, of 
late, I may mention, been found in Ireland by M’Coy. 
Taking leave of the interesting shale deposit at Drummuck, 
I scaled the southern side of the little valley in which it oc- 
curs, and came down upon the range of bold limestone cliffs, 
whose picturesque appearance, rising high over the woods, 
had, at the distance of several miles, attracted my notice, in 
the valley of the Girvan. The relations of this limestone to 
either the indurated sandstones or the trilobite shales, is, from 
the covered character of the ground, not distinctly traceable ; 
but its fossils belong to the Lower Silurian group, and it is 
identical in structure and appearance with a limestone which 
crops out in several localities to the south of the valley, and 
which, underlying the sandstone, is evidently the oldest deposit 
in the district. It is an exceedingly hard sub-crystalline stone, 
and looks as if an outburst of the trap rocks which rise around 
it, and at certain points send out enormous dikes into its sub- 
stance, had given it, for the purposes of the palzontologist, 
rather too much of the fire. And so, though it abounds in 
fossils, — corals, trilobites, and shells,—they are rarely suffi- 
ciently distinct enough to be identified. Occasionally, how- 
ever, on the argillaceous surfaces of the thick beds of which 
the rock consists, we find a trilobite or shell impressed with 
characters sufficiently legible ; and its more massive corals and 
encrinal stems are, from their lighter color, and the trace which 
they still retain of internal structure, usually distinguishable 
enough in the body of the stone. It is a curious circumstance, 
that not only in the group do the fossils of this rock resemble 
