256 ON GLACIERS IN GENERAL. 



structure is the external symbol of this forced internal motion 

 of a body comparatively solid, we may mention one very 

 striking instance recorded by the present writer, as observed 

 on the Glacier of La Brenva, on the south side of Mont Blanc, 

 subsequently to the publication of his principal work on the 

 subject. In this case the ice of the glacier, forcibly pressed 

 against the naked rocky face of an opposing hill, is turned into 

 a new direction ; and in thus shoving and squeezing past a pro- 

 minence of rock, he observed developed in the ice a " veined 

 structure " so beautiful, that " it ,was impossible to resist the 

 wish to carry off slabs, and to perpetuate it by hand specimens." 

 This perfectly developed structure was visible opposite the 

 promontory which held the glacier in check, and past which it 

 struggled, leaving a portion of its ice completely embayed in a 

 recess of the shore behind it. Starting from this point as an 

 origin, the veined laminae extended backwards and upwards 

 into the glacier, but did not spread laterally into the embayed 

 ice. They could, however, be traced from the shore to some 

 distance from the promontory into the icy mass. The direction 

 of lamination exactly coincided with that in which the ice must 

 have moved if it was shoved past the promontory at all. That 

 it did so move was made the subject of direct proof, by fixing 

 two marks on the ice opposite the promontory, one on the 

 nearer, the other on the farther side of the belt of ice which 

 had the lamination best developed. The first mark was 50 

 feet from the shore, and moved at the rate of 4*9 inches daily ; 

 the other mark was 170 feet farther off, and moved almost 

 three times faster, or 14'2 inches daily. Throughout this 

 breadth of 170 feet there was not a single longitudinal crevasse 

 which might have facilitated the differential motion. A paral- 

 lelogram of compact ice, only 170 feet wide, was therefore 

 moving in such a manner, that, whilst one of its sides advanced 

 only a foot, the other advanced a yard. No solid body, at 

 least no rigid solid body, can advance in such a manner ; it is 

 therefore plastic, and the veined structure is unquestionably 

 the result of the struggle between the rigidity of the ice and 



