218 On the Alpine Glacier, Iceberg, [No. 159. 



counted for by so local a cause as the former greater elevation of the 

 Alps. 



To explain these difficulties, M. Agassiz repudiates the former 

 greater elevation theory; and supposes a former colder state of 

 climate prevailing over the countries, in which the phenomena of 

 boulders are found, and which covered them, as is now the case in 

 Greenland, with sheets of ice and glaciers. 



He supposes that most of the large longitudinal beds of unstratified 

 gravel we see in the North and West of England, Scotland and Ire- 

 land, to be the lateral moraines, and the conical truncated mounds 

 and insulated tumuli to be the terminal moraines of ancient glaciers, 

 (left by their retreat, and not pushed forward by them as supposed by 

 Charpentier,) broken and washed by debacles occasioned by the thaw- 

 ing of the ice, masses of which were thus drifted in diverging direc- 

 tions, conveying the large insulated angular masses of rock called er- 

 ratic blocks to the strange situations we now see them occupying. 



Circles of such angular blocks seen round the summits of conical 

 peaks are supposed to be occasioned by the glaciers lodging on it and 

 melting on it. They are usually called perched blocks. 



The rounded or bouldered blocks and gravel are supposed to have 

 been produced by the trituration of the masses of ice and glaciers 

 upon the subjacent surface, and the angular blocks which are found 

 on the surface of the rounded materials, to have been left there by the 

 melting of the ice. The interstratified deposits of mud, gravel and 

 sand are considered to be a re-arrangement of the smaller materials of 

 a moraine produced by the water resulting from the melting of a 

 glacier. M. Agassiz observed polished surfaces, furrows, cavities, and 

 striae in the rocks of England, &c. where the boulder formation ex- 

 ists, similar to those in the Alps, and considers them also as proofs of 

 the former existence of glaciers in those now temperate regions. 



The longitudinal furrows, &c. were observed by Seffstrom and others 

 to have a general direction of N. W. and S. E. in the rocks of Lapland, 

 Norway, and Sweden ; which, added to the circumstance of blocks of 

 granite confessedly from the mountains of Scandinavia being found im- 

 bedded in the boulder and drift of the eastern coast of England and 

 Scotland, over Russia and Germany to the borders of Holland, and 

 other reasons, induced many distinguished geologists to suppose the 



