306 Report of the Researches of M. A^assi^. 



letters : new proof this how difficult it is to guard against the 

 tendency of our minds to confound phenomena as identical, 

 which have only an external resemblance. It is probable that 

 if Professor Forbes had been loss preoccupied with the vast 

 importance of the blue bands which he was in the habit of re- 

 garding as his exclusive domain, he would not have hazarded 

 so unsatisfactory an explanation. After having viewed from 

 the height of some commanding summit the out-croppings of 

 the strata, he should have descended to the neve, and then fol- 

 lowed the windings of the same lines he had before observed, 

 compared and sketched when above them, and he would then 

 have soon been convinced that these lines have nothing in 

 common with what he has designated the ribboned struc- 

 ture, answering to our blue lines, but that they are truly real 

 strata. He would have seen, in particular, that at the limit 

 of these out-croppings the strata are distinctly separated, and 

 that he might there readily introduce a knife, or any other 

 slender body, to a considerable depth. 



Assuredly, nothing is more natural than the presence of 

 these strata or beds in the glacier. Every winter there falls 

 in the higher regions nearly an equal quantity of snow. To- 

 wards spring, when the temperature begins to increase, and 

 when alternations of thaw and frost occur, there is formed on 

 the surface of this bed a hard crust, which becomes thicker in 

 proportion as the frost and thaw are more frequent. This 

 frozen crust on which the dust upborne by the winds and tem- 

 pests of summer descends, separates the bed of the former 

 winter from the covering of snow which falls the ensuing one ; 

 whence it results that, in the hollows of the great circuses, all 

 the beds are separated by beds or zones or lamina? of ice more 

 or less tarnished and soiled. As thus the quantity of snow which 

 falls in these elevated regions is nearly the same every year, 

 as remarked by the mountaineers, what more natural than 

 that the superimposed strata should be of nearly the same 

 thickness *? The idea that these beds are annual deposits, 

 occurs spontaneously to the mind ; it is the opinion generally 

 entertained by the inhabitants of the Alps ; and no naturalist 

 that I know has hitherto thought of questioning its accuracy. 



We sometimes, nevertheless, observe striking irregularities 



