in the Middle Begion of Scotland. 



181 



The rock E, consists of beds of conglomerate and sand- 

 stone dipping to the west at an angle of 5° or 10°. The ra- 

 vine at the Bridge of Allan is from 150 to 200 feet deep. C C 

 is a deposit of clay, of which the lower half has distinctly the 

 chai'acter of the older diluvium, being very firm, and inclosing 

 striated blocks of chlorite slate and other travelled stones. 

 It descends to the water-course at a, and the deep cut b r c 

 made on it for the railway, which occupies the hollow r, as- 

 sures us that the clay is not a mere superficial covering which 

 may have slid down from above and concealed the face of the 

 rock, but the remnant of a deposit which once filled, or 

 nearly filled, the ravine. The depth, in the direction r c, 

 is, at least, 80 feet. The rock is not visible on this side, but 

 it reappears in a quarry half a mile westward with the usual 

 dip, at an elevation exceeding that of the point c, and is also 

 seen on the left of the railway farther north. The legitimate 

 conclusions deducible from the facts, I think, are these; that 

 the ravine was excavated in the rock by a river, and nearly to 

 its present depth ; that the land then sunk under the sea, 

 and remained there during the deposition of the older and 

 newer boulder clay, which filled up the ravine wholly or par- 

 tially ; that after this the land rose again above the water, 

 when the river sought out and re-opened its old channel. 



Examples of similar phenomena are probably not rare. 

 There is a mass of dark coloured clay, 40 feet in height, 

 forming the south bank of the Water of Leith at Coltbridge, 

 which seems to indicate that that portion of the bed of the 

 stream was excavated before the diluvium was deposited. It 

 is alluded to in Sir James Hall's paper. In the parish of 

 Muiravonside, westward from Linlithgow, the River Avon 

 flows between two precipices of the old boulder clay from 100 

 U) 150 feet in height. For Ihe space of a mile above Side. 



