Page:Quarterly Journal of the Geological Society of London, vol. 33.djvu/850

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.]