Ice- Falls and Ice- Rapids. 179 



scending surface, gashed, however, hy thousands of crevasses, as 

 shown in plate 20, to the end of the Pinnacle pass cliffs. • It 

 there finds a more rapid descent, and becomes crevassed in an 

 interesting way. The slope is not sufficient to be termed a fall, 

 but causes a rapid in the ice-stream. 



The change of grade in the bed of the glacier is first felt about 

 a mile above Camp 14. A series of crevasses there begins, which 

 extends four or five miles down-stream. At first the cracks are 

 narrow, and trend upstream in the manner usual with marginal 

 crevasses. Soon the cracks from the opposite sides meet in the 

 center and form a single crevasse, bending upstream in the middle. 

 A little lower down, the crevasse becomes straight, showing that 

 the ice in the center of the current flows more rapidly than at 

 the sides. The more rapid movement of the center is indicated 

 by the form of the crevasses all the way down the rapid. After 

 becoming straight they bow, in the center and form semi-lunar 

 gashes, widest in the center and curving up-stream at each ex- 

 tremity. Still farther down they become more and more bent 

 in the center and at the same time greatly increased in breadth. 

 Still lower the curve becomes an angle and the crevasses are 

 V-shaped, the arrow-like point directed down-stream. These 

 parallel V-shaped gashes set in order, one in ft-ont of the other, 

 are what gives the glacier the appearance of " watered " ribbon 

 when seen from a distance. 



With the change in direction and curvature of the crevasses, 

 there is an accompanying change in color. The cracks in the 

 upper part of the rapid are in a white surface and run down into 

 ice that looks dark and blue by contrast. Lower down, as the 

 cracks increase in width, broad white tables are left between 

 them. Cross-fractures are formed, and the sides of the table- 

 begin to crumble in and fill up the gaps between. As the sur- 

 face melts the tables lose their pure whiteness and become dust- 

 covered and yellow ; but the blocks falling into the crevasses 

 expose fresh surfaces, and fill the gulfs with pure white ice. In 

 this way the color of the sides of the crevasses changes from deep 

 blue to white, while the general surface loses its purity and 

 becomes dust-covered. Far down the rapid where the V-shajDed 

 crevasses are most pointed, the tables ■ have crumbled away and 

 filled up the gulfs between, so that the watered-ribbon pattern 

 is distinguished by color alone. The scars of the crevasses 

 formed above are shown by white bands on a dark dust-covered 



