94 Correspondence — Mr. D. Mackintosh. 



ME. CEOLL OK THE DISPEESION OF BOULDEES. 



Sir, — It is with reluctance that I crave space for a few remarks on Mr. CroU's 

 article, but I think it desirable that some of the difficulties with which his theory 

 seems to be beset should be stated without unnecessary delay. 



Difficulties connected with Physical Geography. — The ground "W.S.W. of "Wasdale 

 Crag does not rise to a sufficient height to have enabled it to generate or give a 

 direction to an ice-stream capable of carrying blocks from Wasdale Crag over the 

 Pennine chain. In the case of an ice-stream assailing the Lake District from an 

 external source, the questions arise — How was it propelled across the ridges and valleys 

 intervening between the Irish Sea and "Wasdale Crag ? "Where was the originating 

 high ground situated ? Or, if the stream came from a Polar ice-cap in a southerly 

 direction, how was it diverted towards the E.N.E. ? These difficulties Mr. CroU may 

 be able to explain, but I cannot see how his theory can be reconciled with the follow- 

 ing facts. 



Prevailing Direction of Glaciation.- — As Mr. CroU surmises, many instances of 

 glaciated rock-surfaces showing the passage of ice across tbe N. of England in an 

 E,N.E. direction may possibly yet be found at high levels, but the fact ought not to 

 be overlooked that most of the high-level instances hitherto discovered do not trend 

 in the above direction, but nearly at right angles to it, or in approximately opposite 

 directions (instances — Gaythorn Tileworks, N. and S. ; watershed between Kentmere 

 and Long Sleddale, N. and S-. ; ' many roches moutonnees north-east of Windermere, 

 glaciated from N.N.W. ; Coniston Old Man, near Copper Works, N. and N.N.W. ; 

 south of Pudding Cove, nearly N. ; entrance of Low "Water Cwm, glaciated from be- 

 tween E. and N.E., at a height of nearly 2,000 feet above the sea). At lower leve"&, 

 between Kentmere and the Irish Sea, the glaciation in nearly every instance I have 

 yet seen has come from points of the compass between N. and N.W. (see article, 

 Geol. Mag. for October, 1870) ; in a very few instances //ww between N. and E.N.E., 

 rather than towards these points. What seems to be the original glaciation, indicated 

 by small parallel undulations, has generally come from between N. and N.N.W., 

 instead of trending in the direction of Mr. CroU's supposed ice-sheet. 



Direction of Drift-carriage. — Between Wasdale Crag and the Pennine chain, the 

 direction in which the drift has been carried varies from N. round by E. to S., though 

 the part of the drift which found its way over Stainmoor travelled E.N.E. Between 

 Wasdale Crag and the Irish Sea, the direction is generally from N. to S., or from points 

 between N.W. and N.E. In many instances the drift-carriage has crossed the striae at 

 greater or less angles. The Eskdale granitic drift, in a matrix of Boulder-clay, crosses 

 the most splendid specimen of glaciated rock-surface I have yet anywhere seen. On the 

 coast adjacent to Blackcombe, the granite, from the N., is found in the three drifts (lower 

 Boulder-clay, middle sand, and upper Boulder-clay), and these three drifts would appear 

 to represent the main part of the glacial period in the Lake District, so as to render 

 it highly improbable that any land ice-stream from the Irish Sea could ever have 

 flowed E.N.E. to Wasdale Crag. On the supposition that the Eskdale drift, and the 

 nearly parallel Criffell drift,^ were carried by a stream of land-ice, the channel of the 

 Irish Sea must have been partly or wholly iilled up to a great height by this stream, 

 as Mr. Eccleston has found blocks of Eskdale-fell granite more than 1,000 feet above 

 the sea on the west side of Blackcombe, and this stream must have carried the granite 

 as far south at least as Bridgenorth and Wolverhampton. On the Pennine hills, and in 

 the Yorkshire valleys, south of the latitude of Wasdale Crag, the drift-carriage has either 

 approximately followed the' valleys, or come chiefly from the N.W. or N.N.W.,^ if we 

 except chalk-flints, which may possibly have come from Ireland. Fragments of 

 Wasdale Crag granite are found in the brown Boulder-clay west of Eipon, and, 

 according to Mr. Green, F.G.S., a boulder of this granite may be seen at Eoyston, 

 near Barnsley. 



Connection between the Direction of Drift-carriage and Altitude. — Though the 

 Granite in the Wasdale area rises to a height of about 1,600 feet above the sea on 



1 Mr. Rutley has found strise near Skeggles Water, running nearly E. and W. (Geol. Mag. 

 for December, 1870). 



2 Mr. CroU's theory, to be satisfactory, ought to embrace an explanation of the dispersion of 

 Criffell granite as far at least as Cliburn (near Penrith), and nearly the whole way uphill, or in 

 opposition to the drainage of the country. 



3 On the north side of Kombald's Moor, however, Millstone-grit has been beautifully smoothed 

 and striated W. and E. at a height of about 900 feet above the sea. 



