SUBJECT CONTINUED. 151 



through the snow accumulated there, convert 

 the lower portion into layers of ice, and the upper, 

 through which it had percolated freely, into a 

 granular substance. This process is repeated 

 year after year, each one adding new layers 

 of ice to that of the preceding, until, in the 

 course of time, a mass arises in height and 

 extent to that precise point at which either 

 the sun's rays obtain access to its surface and 

 prevent a further increase ; or the progressive 

 motion of the glacier, (admitting the possibility 

 of such a motion in the Arctic regions,) ad- 

 vancing upon an inclined plane, gradually brings 

 a lower portion of the berg forward, there to 

 receive its perpendicular increase. In extent, 

 we may imagine the glacier to be limited by 

 the work of destruction that is going on through- 

 out the summer along the whole line of its 

 facial surface by the breaking away of frag- 

 ments, which are precipitated into the ocean 

 whenever the dimensions of the glacier exceed 

 a given limit ; and thus we may imagine the gla- 

 cier to be kept in check both in its vertical and 

 longitudinal extent. 



Professor Leslie, writing upon the formation 

 of icebergs, has given a neat and elegant theory 

 to account for their increase. He pre-supposes 

 the berg to be partly immersed in the ocean, 



