MOUNT LINCOLN. 107 



porphyritic or coarser-grained modification of the Silverheels type, with no 

 glass inclusions or other characteristics of Tertiary \olcanics 



Lincoln Massive. The Mount Lincoln massive, as is shown on the map and 

 as may be seen in the sketch given in Plate IX (page 95), is divided by a deep 

 glacial gorge, heading at the base of Mount Cameron, into two mountain 

 masses : that of Mount Lincoln on the north and that of Mount Bross on 

 the south. On the east face of either of these mountains are two smaller 

 glacial amphitheaters, to which the names of their respective peaks have 

 been given. The beds of each of these three gorges stand at a much higher 

 level than the adjoining beds of the Platte and Buckskin gulches; and, if 

 the glaciers which once filled them were ever directly connected with the 

 main Platte glacier, later erosion has removed evidences of this fact. At 

 all events, it is apparent that after the Glacial epoch, when the ice was 

 gradually receding, these were separate glaciers or neVe" fields. This fact 

 is more particularly manifest in the Lincoln amphitheater, in the middle 

 of which stands a moraine ridge, outlined in the sketch above mentioned, 

 which ends abruptly at the lower end of the amphitheater, about 700 feet 

 above the level of Platte Valley. These amphitheaters have more signifi- 

 cance geologically than their topographical importance would indicate, 

 inasmuch as erosion, having once cut through the overlying and more 

 resisting mantle of sedimentary beds, has carved deeply into the underly- 

 ing Archean, leaving characteristic semicircular walls at their he.ads^ which 

 afford most useful sections for studying the interior structure of the mount- 

 ain mass. 



Mount Lincoln itself has three spurs stretching out to the eastward: a 

 northeastern, an eastern, and a southeastern. Lincoln amphitheater is 

 included between the two first. The surface of these spurs is covered by 

 beds of the Paleozoic system, dipping eastward at an angle of 10 to 15. 

 This is the average inclination of the beds over the main portion of the 

 mountain mass; but, as already mentioned in the case of Quandary Peak, 

 the dip becomes steeper on the extreme eastern flanks. In general, how- 

 ever, the slope of the spurs themselves steepens for a short distance more 

 rapidly than the dip, in consequence of which there is a belt of lower beds 

 exposed along the foot of the steeper slopes. 



