142 



CRUISE OF STEAMER CORWIN IN THE ARCTIC OCEAN. 



southeast, thus making the island about 6 miles long, the average width being about 2 miles. 

 Near the middle of the island there is a low gap, where the width is only about half a mile, and 

 the height of the summit of this portion of the watershed between the two sides is only about 

 2.10 feet. The entire island as far as seen is a mass of granite, with the exception of a patch of 

 metamorphic slates near the middle, and no doubt owes its existence with so considerable a 

 height to the superior resistance it offered to the degrading action of ice, traces of which are 

 presented in the general moutonnee form of the island, and in the smooth parallel ridges and 

 valleys trending north and south. These evidently have not been determined as to size, form, 

 position, or the direction of their trends by subsidences, upheavals, foldings, or any structural 

 peculiarity of the rocks in which they have been eroded, but simply by the mechanical force of 

 an overs weeping, all embracing ice sheet. 



The effects of local glaciers are seen in short valleys of considerable depth as compared with 

 the area from which their fountain snows were derived. We noticed four of these valleys that had 

 been occupied by residual glaciers; and on the hardest and most enduring of the ups welling rock 

 bosses several patches of the ancient scored and polished surface were discovered, still in a good 

 state of preservation. That these local glaciers have but recently vanished is indicated by the 

 raw appearance of the surface of their beds, while one small glacier remnant occupying a shel- 

 tered hollow and possessing a well-characterized terminal moraine seems to be still feebly active 

 in the last stage of decadence. 



HERALD ISLAND. 



This small granite island standing solitary in the Polar Ocean we regard as one of the most 

 interesting and significant of the monuments of geographical change effected by universal 

 glaciation. 



Our stay on Yvrangel Island was too short to admit of more than a hasty examination of a few 

 square miles of surface near the eastern extremity. The rock format ion is a close-grained clay slate, 

 cleaving freely into thin Makes, with occasional compact metamorphic masses rising above the gen- 

 eral surface or forming cliffs along the shore. The soil about the banks of a river of consider- 

 able size that enters the ocean here has evidently been derived in the main from the underlying 



BED (IK SMALL RESIDUAL GLACIER ON SAINT LAWRENCE ISLAND. 



slates, indicating a rapid weathering of the surface. A few small deposits of moraine material 

 were discovered containing traveled bowlders of quartz and granite, no doubt from the mountains 



