294 



Correspondence — Mr, George Maw, 



at Candren, two at Walkingshaw, five at Blythswood, and one in the 

 bed of the Clyde at North Barr House, went through Boulder-clay 

 alone, by which we learn that, as the ground is flat, they were sunk 

 in what are now subterranean hillocks, but which were once sub- 

 marine islands or shoals in a sea, depositing mud around them. 

 Seventeen bores — two at Candren, nine at Walkingshaw, one at 

 Blythswood, three at the Barns of Clyde, and one at Blairdardie, 

 went through sand and mud only, the silt of the glacial sea filling 

 up the hollows between the submerged hillocks or shoals. The 

 deepest of these bores are at Walkingshaw, one being 152 and 

 another 159 feet deep ; and one, at Shiels, above Kenfrew, 144 feet 

 deep, and the remainder from 80 to 100 feet deep. Nineteen bores 

 have more or less Boulder-clay, sometimes only a few feet, at other 

 times more than half. At Craigielee, near Paisley, and Gamieland, 

 near Eenfrew, rocks come above ground, and these must have 

 been sunken rocks at that time, against which, doubtless, many 

 an ice-berg struck. From these facts it is clear that the bottom of 

 the glacial sea was extremely imdulating, as much so as any modem 

 land surface. Into the hollows of the mud of the glacial sea the 

 washings of these very hillocks were deposited, and in them lived 

 the boreal shells which have made this region so famous in Post- 

 Tertiary geology. J. A. 



coi^e»:bs:fo3^x)E3^ce. 



I.— HORIZONTAL PRESSURE AND VERTICAL DISPLACEMENT. 



Sir, — In the March number of the Magazine I made a few ob- 

 servations on the probable connection between the vertical force of 

 gravitation in a sphere with the horizontal force that appears to 

 have produced slaty cleavage. 



The converse of this proposition is well illustrated in the dis- 

 tortion of an old brick wall at Shiffnal, in this county, represented 

 in the accompanying engraving, in which the coping has risen from 



its vertical support and ranged itself into an arch, leaving a vacant 

 space underneath. The mortar joints had evidently been expanded 

 by frost, the length of the coping thereby increased, and the expan- 

 sion being horizontally resisted, the increased length was compelled 

 to expand itself as a curve. 



The case seems strictly analogous to what might take place in the 



