310 D. Mackintosh — The Drifts of the Lake District. 



tinuation of the sand and gravel ridges further north, and the Carn- 

 fortk sand and gravel knolls further south. 



The ridges under consideration are, generally speaking, not linearly 

 parallel. In the same line an oblong hollow is succeeded by an 

 oblong eminence, as if the eminence had been partly formed by the 

 abstraction of matter from the hollow, but this may not necessarily 

 have been the case. Most of the stones and boulders as far S. as 

 Yealand have come from about N.N.E., and consist chiefly of upper 

 Silurian grit or mudstone, and some porphyry, breccia, and dark 

 felstone (from near Wasdale Crag, ?). At Carnforth, further S., the 

 stones and boulders are nearly all limestone, which likewise pro- 

 bably came approximately from the N. 



From these facts it may be inferred that the ridges may possibly 

 represent three periods — the period when the rocky nuclei were 

 formed by denudation — the period when the Boulder-clay was ar- 

 rested by these nuclei — and the period when the sand and gravel 

 which partly or entirely compose the ridges were deposited. How- 

 ever this may be, it may, I think, safely be asserted that the present 

 aspect and parallelism of the ridges is due to the agency which de- 

 posited the sand and gravel, or to marine currents with or without 

 floating ice ; and this view of their formation may be applied to the 

 curved parallel ridges which ramify like a fan from the neighbour- 

 hood of Wasdale Crag, and which have probably been finally shaped 

 by the current that distributed the granitic boulders. 



Southerly Extension of the Great N. Western Drift. — ^The Wasdale 

 Crag and Carnforth^ drift-stream would appear to have nearly, if not 

 altogether, terminated a little S. of Lancaster. Some distance further 

 S. the ground was monopolized by the great drift stream from the 

 N.W., already described. This stream may have received some 

 slight contributions from the N.N.E. stream. Among the boulders 

 exhibited in Peel Park, Salford (nearly all of which were found in 

 the neighbourhood), I detected many old Cumberland acquaintances. 

 The following is a rough estimate of the relative per-centage of the 

 larger boulders, which I made with the assistance of Mr. Plant, 

 r.G.S. : — Felspathic trap running into porphyry and breccia, 50 ; 

 Silurian grit (apparently from Furness) and local sandstone, 30 ; 

 Eskdale fell granite, 19; Criffell granite, 1;=100. To the east of 

 Manchester I have seen no Criffell granite. At Snape Green brick- 

 yard, near Southport, the Criffell seemed to preponderate over Esk- 

 dale granite. (For further remarks on the southerly extension of the 

 north-western drift see explanation accompanying the Map, p. 312.) 



General Besults. — From the facts stated in the eight articles I have 

 written on the Drifts of the N.W. of England,'^ I think it may be 



^ The finest sections of sand and gravel I have yet seen are at the Carnforth Rail- 

 way Station, and on the Canal side. At the latter place there is gravel above and 

 below, and sand in the middle. At the village, a great deposit of sand contains 

 enormous limestone boulders, one of them 9|x9|x5 feet. In addition to limestone, 

 in the Carnforth drifts, there are Silurian grits and volcanic rocks from about N.N.E., 

 and Carboniferous grits, etc., from the N.E. 



2 Geol. Mag., August, October, December, 1870, and February, June, and July, 

 1871 ; Proceed. W. Riding Geol. Soc, 1870; Quart. Journ. Geol. Soc. vol. xxv. 



