136 A. Mil ward, Esq., on the 



give rise to a prima facie presumption, that ridges are to be 

 looked for in an earlier stage of that viscous fluid also \ Is 

 not the analogy just so far strong enough as to induce us to 

 examine whether there is any trace of such ridges or waves ; 

 and, if so, whether their correspondence with the alternations 

 of porous and compact ice is sufficient to account for the lat- 

 ter? 



It is evident that such ridges or waves, if they do exist, 

 must be very slightly marked, or they would not have been 

 overlooked ; but then, it is to be remembered, that the dif- 

 ference between the two kinds of ice is also very slight, — in 

 fact, only barely apparent. It will be useless to look for 

 them at the lower parts of glaciers, as they will have disap- 

 peared under the effects of atmospheric and other action 

 through the lapse of many years, which will have degraded 

 any existing ridges, just in the same way as in the case of 

 outcropping strata. 



There is also a tendency to the establishment of an equili- 

 brium as to elevation, to say nothing of the disturbing effect 

 of the lateral friction. It is, therefore, towards the head of 

 the glacier, where the true glacial structure commences, that 

 we are to look for such ridges : the best time, also, will be at 

 the commencement of summer, after the disappearance of 

 the snow, and before the confusion of the surface occasioned 

 by the sun's influence. 



1. It has been suggested to me, that in the case of the 

 mud-slide, there may be an original difference of consistency 

 in the bands of mud, which is only increased by the action of 

 the drainage water ; and that the ridges and intervals are 

 the outcropping of these beds which compose the mud- stream. 

 If there be such a tendency in viscous fluids to separate into 

 beds of different consistency, such a difference of consistency 

 may exist in glaciers, although the actual ridges may never 

 be sufficiently developed to be apparent. Such a peculiarity 

 of viscous structure would account for the bands of porous 

 and compact ice, whether the ridges be found or not. 



At present, however, we have no proof of such an internal 

 structure, and may therefore dismiss it. 



2. If, however, ridges or waves are found to exist, the case 



