360 CHARACTER OF THE DRIFT. chap. xvin. 



The annexed drawing represents one of the best known of 

 train No. G, being that marked n on the map, p. 357. Ac- 

 cording to our measurement it is fifty-two feet long bj^ forty 

 in width, its height above the drift in Avhich it is partially 

 buried being fifteen feet. At the distance of several yards 

 occurs a smaller block, three or four feet in height, twenty 

 feet long, and fourteen broad, composed of the same compact 

 chloritic rock, and evidently a detached fragment from the 

 bigger mass, to the lower and angular part of which it would 

 fit on exactly. This erratic n has a regularly rounded top, 

 worn and smoothed like the rochcs moutonnees before men- 

 tioned, but no part of the attrition can have occurred since it 

 left its parent rock, the angles of the lower portion being 

 quite sharp and unblunted. 



From railway-cuttings through the drift of the neighbor- 

 hood, and other artificial excavations, we may infer that the 

 position of the block n, if seen in a vertical section, would be 

 as represented in fig. 52. The deposit c in that section, 

 p. 359, consists of sand, mud, gravel, and stones, for the most 

 part unstratified, resembling the till or boulder-clay of 

 Europe. It varies in thickness from ten to fifty feet, being 

 of greater depth in the valleys. The uppermost portion is 

 occasionally, though rarely, stratified. Some few of the im- 

 bedded stones have flattened, polished, striated, and fui-rowed 

 sides. They consist invariably, like the seven trains above 

 mentioned, of kinds of rock confined to the region lying to 

 the N.W., none of them having come from any other quarter. 

 Whenever the surfixce of the underlying rock has been ex- 

 posed by the removal of the superficial detritus, a polished 

 and furrowed surface is seen, like that underneath a glacier, 

 the direction of the furrows being from N.W. to S.E., or cor- 

 responding to the coui'se of the large erratics. 



As all the blocks, instead of being dispersed from a centre, 

 have been carried in one direction, and across the ridges A, b. 



