Vol. 68.] THE GLACIATION OF THE BLACK COMBE DISTKICT. 405 



buted the distribution of Scottish rocks to boulder-bearing icebergs 

 swept along by marine currents. He also required two separate 

 submergences of the land to account for his facts, although he 

 recognized the active part played by land glaciers in the formation 

 of the boulder-clays. 



Among the writings of T. Mellard Eeade, that upon the Eskdale 

 Drift and its bearing upon glacial geology,^ published in 1893, is of 

 great interest in its relation to the subjects discussed below. In a 

 later (1896) Address ^ he deals with the Low-Level Marine Boulder 

 Clays and Sands between St. Bees Head and Kavenglass. 



Since that time little seems to have been written about the Black 

 Combe area, although Mr. G. W. Lamplugh drew a comparison 

 between the drift-plain west of Black Combe and the northern 

 drift'plain of the Isle of Man.^ 



II. Geological Stetjcttire. 



The district examined may be divided in a broad way into three 

 main physiographical divisions, from east to west, as follows : — 

 (1) The Duddon Yalley and Estuary, (2) the mountainous tract 

 between the Duddon Yalley and the plain, (3) the low plain at the 

 foot of the mountains, and bordering the sea between Millom and 

 Bavenglass. 



In the greater part of the Duddon Yalley, and over the mountain 

 tract, the glacial drifts have merely modified the pre-existing topo- 

 graphy, but the third district — the plain — is almost entirely com- 

 posed of drift deposits of considerable thickness, which descend 

 below sea-level beneath a large part of the plain's surface extent. 



Near Kirksanton and MiUom in the south, some low ground 

 is occupied by Carboniferous Limestone. North of Silecroft the 

 formations beneath the plain are considered to be of Triassic age ; 

 but, with the exception of one exposure mapped by Aveline near 

 Corney Hall, north of Bootle, there is no visible outcrop of these 

 rocks. 



The mountain country consists chiefly of three distinct types of 

 rock : namely, slate, volcanic rocks, and granite. An inlier of so- 

 called ' Skiddaw Slate,' roughly triangular in shape, and 12 or more 

 square miles in extent, forms a group of fells reaching a height 

 of 1969 feet at Black-Combe summit. The bulk of this mountain 

 consists of blue-grey slates of felspathic appearance, tremendously 

 compressed and very highly cleaved, the cleavage-planes dipping 

 generally in a north-westerly direction. In some cases secondary 

 cleavage and pressure has resulted in the production of slates with 

 frilled surfaces and presenting a glossy appearance. Chevron folds 

 and belts of rock riddled with vein-quartz, which coincide roughly 

 with the direction of cleavage, testify also to the tremendous pressure 

 brought to bear upon these rocks. 



1 Geol. Mag. dec. 3, vol. x (1893) pp. 9-20. 



2 ' The Present Aspects of Glacial Geology ' Proc. Liverp. Geol. Soc. vol. viii 

 (1897-1900) pp. 13-31. 



3 ' The Geology of the Isle of Man ' Mem. Geol. Siirr. 1903, p. 366. 



