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Mr. W. H. Pearsall. 



from which run out ridges, radiating like the spokes of a wheel, and 

 gradually decreasing in height as they pass further away from the centre. 

 Practically all the main valleys between these ridges contain one or more 

 lakes, varying greatly in size, but otherwise somewhat similar in appearance 

 and characteristics. It is with eleven of the larger lakes that the present 

 paper deals ; Thirlmere, now practically a reservoir with variable water 

 level, and those lakes smaller than Buttermere, having been omitted for the 

 sake of uniformity. The remaining lakes vary in length from 10'5 miles 

 (16'8 kilom.) (Windermere) to 1-26 miles (2 kilom.) (Buttermere), and have 

 mean breadths of from 0'5 to 0-25 miles (0-8 to 0'4 kilom.). They lie at 

 uniformly low altitudes, Hawes Water, 694 feet (211 m.), being the highest. 

 Our knowledge of their chief sub-aqueous features is due to the work of 

 Mill and Heawood,* from whom the table of their dimensions (Appendix I) 

 is chiefly compiled. 



Origin of the Lakes. — As is well known, the whole of the Lake District was 

 very heavily glaciated during the Ice Age, with the result that soil, surface 

 deposits, and all but the boldest features of pre-glacial scenery, were removed 

 by ice, leaving ' a bare and sterile rock mass, here and there overlaid by 

 moraines and boulder clay. The effects of ice were particularly striking in 

 the valleys. These were deepened and scoured out, the greatest erosion 

 taking place towards the heads of the depressions, where the valleys (and the 

 ice) were deepest. Thus, on the retreat of the ice, a number of rock basins- 

 were left, occupying the lines of the pre-glacial valleys, and tending to have 

 straight steep sides, all minor points having been torn away by the ice and 

 removed, along with any pre-glacial alluvial deposits (see Marr).f 



The present lakes lie in these rock basins, and it may be noticed that the 

 theory of their origin presupposes that their primitive condition was 

 essentially rocky, a supposition borne out by the nature of the shores and 

 islands at the present day. Glacial deposits also frequently exist, often 

 rounded morainic boulders, and sometimes an impervious boulder clay. 

 Neither the presence of these, nor the fact that they may hold up the lake 

 to a higher level (as at Windermere and Bassenthwaite), invalidates the 

 conception that these lakes are essentially rock basins, and are, in origin, 

 of great similarity. 



Modifying Agencies — Wave action produces numerous well marked effects. 

 Along the shores one can typically distinguish three chief zones caused by 

 wave action: (1) the gravel wave-cut terrace just below the water level 

 (2) a comparatively silt-free area of stone or boulder clay, often sprinkled 



* ' Geogr. Journ.' (London), vol. 6, 1895. 



t ' The Geology of the Lake District,' Cambridge, 1916. 



