410 T. V. Holmes — Geological Structure 



and to the latter 140 metres. The two last-named lakes afford, 

 moreover, at their lower ends, typical examples of the formation of 

 lake basins behind the terminal moraines of retreating glaciers, for in 

 both cases the widened basins at the lower ends are appendages of the 

 original fjords, and their contours conform strikingly to those of the 

 concentric moraine walls behind which they were formed. 



The zonal flexure also accounts for the extraordinary depth of the 

 present lake basins as the result of overdeepening by the lowering of 

 their floors, as against the theory of overdeepening by the direct 

 action of glacial erosion, as if such steep, long, and narrow basins 

 could be formed by the vertical scooping of a glacier in the same way 

 as a cirque or corrie. The indirect action of the glaciers was more 

 probably confined to the widening of the fjords and of the tributary 

 valleys of the Dora Baltea, Ticino, Adda, and others. 



The simultaneous operation of the zonal bending and the retreat of 

 the glaciers on the one hand, and the recession of the sea from the 

 Po Valley on the other, must have been of very long duration, 

 probably till the end of the Ice Age, including the period of the last 

 glaciation, which did not reach, and therefore did not directly affect, 

 the contact zone of the sea and the moraine walls in the Po Valley. 



Such extraordinary phenomena as the natural exit of the Como 

 fjord being choked and its drainage reversed, so that the present lake 

 has its only exit through the Lecco arm; or the former connexions 

 between the Como and Lugano fjords at Menaggio and Porlezza, and 

 through the Breggia Valley at Chiasso being severed by the lowering 

 of fjord levels, and the Lugano fjord finding its exit through the 

 Tresa into Lake Maggiore ; or again, Lake Orta having its southern 

 outlet barred and its drainage reversed to the north into the Toce ; or, 

 similarly, Lake Varese draining reversely into Lake Maggiore, — all 

 these phenomena, as well as the labyrinth of erratic and tortuous 

 watercourses throughout the morainic littoral and the whole lake 

 district, are only some of the direct and indirect effects of that great 

 maximum glaciation which has left its impress along the base of the 

 Italian Alps both in Piemont and Lombardy by a morainic landscape 

 in magnitude, grandeur, and variety unequalled in any other part of 

 the Alps or of Europe. 



V. — On the Evidence as to the Geological Structure of 

 Cumberland bordering the Solway. 



By T. Y. Holmes, F.G.S., F. E. Anthrop. Inst. 

 (PLATE XIV.) 



WHILE no doubts have existed among geologists that the rocks of 

 this district are of Permo-Triassic age, that they are surrounded 

 by older formations of the Carboniferous Series, and capped by a small 

 Lias outlier, unanimity as to the relations of the local Permo-Triassic 

 rocks to each other has never yet prevailed. Hence when the 

 Geological Survey Memoir, by the present writer, on this district was 

 published in 1899, Sir Archibald Geikie stated in the preface that the 

 delay in its appearance was due to the hope that additional deep 

 borings might have settled certain questions as to the relations to 



