738 D. MACKINTOSH ON SOME NEW SECTIONS 



Horizontal and Vertical Range of the Middle Drift. — The middle 

 drift of the plain loses the character of a deposit of fine sand and 

 gravel in the neighbourhood of the mountains, where it becomes 

 horizontally continuous with a coarser formation, especially in the 

 upper part, which consists of large rounded stones, often reaching a 

 foot in average diameter. In among the mountains it contains 

 large boulders, some of which are striated. It likewise graduates 

 or dovetails downward into a boulder-clay or loam, by which it is 

 sometimes horizontally replaced. Where it penetrates into the 

 mountain-valleys it gradually loses its shelly character, as if the 

 increased freshening of the sea-water, by melting snow, had proved 

 inimical to the existence of mollusca. The shells hitherto found at 

 high-levels in this country have been limited to the outer slopes of 

 the mountain districts, in positions facing what once must have been 

 comparatively wide and salt seas. 



Is there any " true Till " at low levels in the Basin of the Irish Sea ? 

 ■ — The mere fact that bricks can easily be made out of both the 

 low-lying shelly clays of the basin of the Irish Sea would be looked 

 upon by a Scotch geologist (as I was some time ago assured by an 

 eminent glacialist) as sufficient to prove that they are not " true 

 till," while the enormous distances which the erratic stones found 

 in these clays have been transported would be regarded as corrobo- 

 rative of the idea ; for there is perhaps no point on which glacialists 

 are more agreed than that the constituents of " true till" (including 

 stones) are more or less local. But in one of these clays at Wolver- 

 hampton (I have not yet determined which) Scotch granite is found 

 which must have travelled 170 miles ; and in the lower Boulder-clay 

 of the estuary of the Dee similar granite is found in abundance 

 which must have travelled 100 miles. Scotch granite may be found 

 at Upton-on-Severn, near Worcester, which must have been trans- 

 ported 200 miles (as the Rev. W. S. S3 T monds informs me), or a 

 distance about equal to that between the Moray and Solway Friths ; 

 and I think a consideration of relative levels will show that it could 

 not have been retransported from the southern end of a till- distribu- 

 ting ice-sheet. At New Colwyn Bay, North Wales, and the neigh- 

 bourhood, a very stiff blue clay without shells, and with stones almost 

 entirely local, may be traced along the sea-shore. Above it there is 

 a representative of the base of the lower brown clay, a bed of sand- 

 and-gravel, and the upper clay on the top. The latter contains 

 many erratic stones. This blue clay is apparently on the horizon 

 of the blue clay of the Marron valley, the neighbourhood of Keswick, 

 the Yorkshire valleys, and some parts of Lancashire (where Mr. De 

 Ranee regards it as a clay formed under land-ice). If there is any 

 low-lying " true till " in the basin of the Irish Sea, I think it must 

 be this blue clay. 



[This paper is intended to be introductory to one on the Corre- 

 lation of the Drifts of the north-west of England with those of the 

 Midland and Eastern counties, a task, I believe, which can only be 

 satisfactorily accomplished by one observer going over the whole 

 ground.] 



