BucMey — Ice Ramparts. 155 



ing a period of lowering temperature neither corroborated nor 

 disproved this theory, on account of the difficulty in delineating 

 the boundaries between the old and the new ice. By means of 

 the lamination, which shows at the surface, the veins could be 

 traced about half way through the ice sheet, but at that depth 

 they were always lost. The shaded portion of Plate XVII repre- 

 sents that portion of the vein that could be delineated. How- 

 ever, I am very certain that this does not represent the total area 

 of new ice. The lamination which extends to this depth is prob- 

 ably due to very fine cracks caused by differential contraction 

 which is constantly operating during falling temperatures. 

 During a rise in temperature the ice veins can scarcely be de- 

 lineated to any depth below the surface. Apparently the com- 

 pressive stresses resulting from the rising temperature obliter- 

 ate by regelation the fine cracks formed by tensile stresses dur- 

 ing the time of lowering temperature. 



The actual movement of the ice sheet is further shown by 

 faults, which may have either a horizontal or vertical displace- 

 ment. When relief takes place by the formation of ramparts 

 along the shore horizontal displacement takes place in the ice 

 sheet. When relief takes place by the arching up of the ice 

 sheet, both vertical and horizontal displacements result. Plate 

 XVIII. shows a fault with a horizontal displacement of about 

 two feet. The crack which formed normal to the first one and 

 along which the displacement occurred, as shown in the illustra- 

 tion, may have been initiated prior to the time of expansion, or 

 it may have resulted from the expansion of the ice at the time 

 of relief. The displacement of two feet in the above illustra- 

 tion is evidence that a corresponding relief must have taken 

 place, either by bowing up of the ice at another place, or by the 

 formation of ramparts along the shore. 



In the detection of* faults in ice, as in rocks, one may easily be 

 led astray by other phenomena which have all the appearance of 

 faults. It often happens that a crack will terminate abruptly 

 against another cross fracture and continue again on the other 

 side at a distance of from two inches to two feet from the place 

 where it terminates. ^N^umerous secondary cracks are fre- 

 quently observed to end abruptly against one of larger size. 



The most complex fracturing and faulting occurs when -relief 



