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Downloaded from http://pygs.lyellcollection.org/ at University of Iowa on July 3, 2015 401 SOME OBSERVATIONS ON THE GLACIAL GEOLOGY OF FURNESS. By GEORGE GRACE, B.SC, A.R.C.SC, and FREDERICK HOWARD SMITH, B.SC. (Read on March 29th, 1922.) For the purposes of this paper Furness may be taken as that portion of the Lake District which is bounded on the west by the River Duddon, on the north by the Little Langdale, and on the east by Windermere and the River Leven. Within this area the solid geology, so far as it affects the glacial geology, is very simple. If a line be drawn from Duddon Bridge in a north-easterly direction through Coniston and forward, it will cut off a north-westerly portion composed of Ordovician volcanic rocks of the Borrowdale series, and leave a south-eastern area chiefly made of Silurian slates and grits. Although there are minor variations in the dip and strike of these rocks, they may be regarded as having a general strike parallel to the dividing line mentioned, and a dip towards the south-east. The volcanic area consists of a mountainous massif, culminating in the Coniston Old Man (2633 ft.), and running to the south-west until it is cut off by the Duddon estuary. The south-east area is divided naturally into a hilly portion in the north, reaching in several places to 1000 feet, and a much flatter area, south of Ulverston, generally known as Low Furness, much of which is below the 50 feet contour. Very little attention appears to have been given to the glacial geology of Furness for many years. Clifton Ward* published details of the glaciation of the southern Lake District in 1875, but stopped at the northern boundary of Furness, and no one appears to have con• tinued his work. We have failed to find any systematic description of the glaciers of High Furness, although their general courses seem to have been common knowledge, and are referred to by many writers, notably by Prof. Marr in his " Geology of the Lake District." Most of the details we give in the following paper appear to be quite new. The drifts of Low Furness and, to a certain extent, of High Furness, were dealt with by Mackintosh,")" who gives a full and accurate account * Quart. Journ. Oeol. Soc, Vol. XXXI. (1875), pp. 152-165. f Quart. Journ. Geol. Soc, Vol. XXV. (1869), pp. 407-431 ; Vol. XXIX. (1873), pp. 351-359; and Vol. XXX. (1874), pp. 174-179. Downloaded from http://pygs.lyellcollection.org/ at University of Iowa on July 3, 2015 Proc. Yorks. Geol. Soc, Vol. XIX., Plate XLVIII. THE ROUNDED SUMMITS OF THE CONISTON OLD MAN RANGE. VIEW DOWN RED DELL, SHEWING STEP INTO LOWER VALLEY. 'To face page 401. Downloaded from http://pygs.lyellcollection.org/ at University of Iowa on July 3, 2015 402 GRACE : THE GLACIAL GEOLOGY OF FURNESS. of them in several papers, but his conclusions are invalidated by bis failure to distinguish between the insular drift and that from the Irish Sea. He seems to have regarded granite as the criterion of Upper Boulder Clay; consequently his Lower Boulder Clay and Middle Series are mostly insular drift. The same confusion occurs in J. D. Kendall's* paper in 1880. B. Smith,t in his paper or the Glaciation of the Black Combe District, deals with some of the phenomena produced by the ice at the head of the Duddon estuary, and his observations seem to fit consistently with those recorded below. In the latter part of his paper he suggests " that the water accumulating in the Duddon estuary must have escaped somewhere to the south along the coastline of Furness." This has turned out to be an accurate forecast of what we have found. THE PRE-GLACIAL CONDITION OF FURNESS. It is generally admitted that at the beginning of the Glacial Period the Lake District had been above sea level for a considerable period, and that the agents of normal denudation had been at work for a sufficient time to reduce it to what Prof. Davis has termed an area of " Subdued Relief." The present condition of High Furness is very far from this type of topography, and must be regarded as, largely, the product of the abnormal erosion of the Glacial Period. The Ordovician area abounds in angular rocky scenery—the well- known vertical crags and canal-like valleys—which are the antithesis of Prof. Davis's flowing curves, while the Silurian area contains several large basin-like depressions not hitherto described, which it is difficult to regard as the result of normal erosion. These are : The Coniston Basin, The Lowick Basin, The Broughton Beck Basin, The Duddon Estuary and its continuation northwards to Woodland. Of these the Coniston Basin is the most important, and we propose, therefore, to discuss its origin in detail. (See map of High Furness, Plate XLIX.). It is composed of two separate valleys, which have originated quite independently. These valleys are a considerable distance apart at their southern ends, but merge into one another in the north. The more westerly is the straight valley running from Woodland to Torver * Quart. Journ. Geol. Soc, Vol. XXXVII. (1880), p. 29. t Quart. Journ. Geol. Soc, Vol. LXVIII. (1912), p. 402-448. Downloaded from http://pygs.lyellcollection.org/ at University of Iowa on July 3, 2015 Proc. Yorfa. Geol Soc, Vol. XIX., Plate XLIX. MAP OF HIGH FURNESS. Downloaded from http://pygs.lyellcollection.org/ at University of Iowa on July 3, 2015 GRACE : THE GLACIAL GEOLOGY OF FURNESS. 403 and continuing, more or less clearly, almost to Coniston Old Hall. This originated as a strike valley, and owes its canal-like aspect to its coincidence with the line of bedding and cleavage of the slates. It is not easy to decide how far it had reached northwards before the in• terference of glacial conditions. The gap through which Torver Beck empties into the lake seems too old to have originated during Glacial times, and, if so, indicates that a stream crossing the valley at this point was not diverted down the strike valley, and that, therefore, the latter had not reached so far. The most probable condition was that, from a col near Haverigg Holme, one stream ran south-west towards Woodland, and another flowed north-east into Torver Beck, and that north-east of the Beck there was no trace of a depression between the Fells and the present lake valley. The eastern valley, where Coniston Lake now stands, cannot be explained so simply. It coincides at the head with a well-marked fault, but this disappears about half way down the lake, so that it does not account for the valley. Also, the present valley cuts across the grain of the rocks, so that it is not structural. It probably originated so long ago that the circumstances which began it have disappeared and cannot be reconstructed. If our reconstruction of the Torver Valley be correct, this eastern valley must have carried the drainage from both Yewdale and the Church Beck Valley, and received the Torver Beck as a tributary near its present confluence. Its straight course, however, suggests that its present form is more due to glacial action than to normal erosion. The slopes on its eastern side are lacking in any suggestion of spurs, such as might have been expected if it had been a normal river valley only slightly modified by glacial action. Also the fact that the side valleys which run into it, viz., the Church Beck Valley, both the branches of Yewdale and the Torver Beck Valley, are all, at some part of their courses, hanging valleys, suggests that the Pre-Glacial level of the stream into which they ran was much higher than now. The profile of the Church Beck has two distinct steps. A smooth curve continuing the highest reaches of the stream seems to point to the old level of the main valley as being between the 300 and 400 feet contours. This estimate is confirmed by the profile of Upper Yewdale, which falls from 500 feet to 300 feet in less than a mile, and by the Guards Beck, which has a similar profile. If this is anywhere near the truth, as the lowest part of Coniston Water is 42 feet below O.D., the Downloaded from http://pygs.lyellcollection.org/ at University of Iowa on July 3, 2015 404 GRACE : THE GLACIAL GEOLOGY OP FURNESS. rock erosion during Glacial times must have been as much as 350 to 450 feet. Originally the Ash Gill Beck and the Torver Beck passed through separate gaps near Torver Park, hut they must have united somewhere near Torver, as there is only one gap leading into the lake. Now, the Torver Beck has captured the lesser stream on the moor, and left its lower course as a dry gap. The bed of the combined streams as it comes down into the present Torver valley is a succession of cascades. Its course across the valley bottom is not in line with its previous course, and suggests that it is making for the gap once used by the Ash Gill Beck. Through this it cascades again into the lake, confirming the suggestion that the valley at Torver originated during Glacial times, and that the present level of the lake is much lower than the pre-Glacial level of the stream into which the Beck ran. The conclusion we draw from these facts, and the details of the Yewdale valley—which have been previously described by Prof.

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