574 Correspondence — /. W. Judd — M. Jespersen. 



iferous strata far beyond what had hitherto been regarded as their 

 northern limits in these islands. 



Second. — It affords a new and very striking illustration of the 

 enormous denudation which must have preceded the outpouring of 

 the Tertiary lavas of Scotland, and of the remarkable series of 

 accidents to which the preservation of many vestiges of the geological 

 formations in the Highlands are due. 



Third. — It gives the geologist a base to the grand series of Poika- 

 litic (Permian and Triassic) rooks in the Highlands. 



Fourth. — It affords us, moreover, another link towards the com- 

 pletion of the ' Geological Eecord ' in the Highlands ; which now 

 embraces representatives of all the great geological formations except 

 the Upper Silurian. 



I must of course postpone the description of these interesting beds, 

 and of their wonderful relations to the surrounding rocks, together 

 with the discussion of , the considerations which their occurrence 

 suggests to the geologist, till the publication of the third part of my 

 memoir, " On the Secondary Eocks of Scotland." 



John W. Judd. 



ASAE. 



SiK, — Will you allow me, a foreign hammerer, to advance in your 

 Magazine a theory on the above-named subject. 



Sweden (and all Scandinavia) was once covered by a sliding ice- 

 sheet, moving towards a lower level. In our days we have no such 

 thing ; the ice-sheet disappeared by being melted away ; indeed, 

 some of it may have been carried off and floated away by a rise 

 in the level of the sea, but not all, for this might require a rising of 

 the sea equal to -^^ the thickness of the ice (1000—7000 feet ?) -f the 

 elevation of the ground, or a rising of several thousand feet. I refer 

 to the last sheet of land-ice, but I do not deny an earlier melting 

 and the existence of icebergs, floating-ice, etc., nor do I deny a sub- 

 mergence of the land. 



This ice-sheet disappeared, I venture to suppose, by melting away. 

 Nor is such general melting of glaciers any strange thing, for we 

 may find it so in the Alps, in Greenland, etc. ; only, of course, the 

 increase is usually equal to the decrease of the ice. 



The melting probably always goes on at the bottom of a glacier 

 — that at the surface mostly during summer-time. 



At the bottom of a large and vast ice-sheet or mer-de-glace, such 

 as that supposed to have covered Sweden, the melting will hardly be 

 uniform all over, but may be heightened, where the ice passes de- 

 pressions in the ground and valleys, especially those with running 

 waters ; along such places, the ice being greatly reduced in mass, 

 there may be a flowing towards it from one or both sides of the 

 ice-sheet, to compensate this loss and want of stability; probably 

 here much detritus was accumulated, either at the bottom, or in the 

 ice, or upon its surface ; and this surface may have had depressions, 

 sometimes with running waters and even lakes, and in these depres- 



