36 G. K. GILBERT — DOMES AND DOME STRUCTURE 



Plate 3. — Dome Structure near Emerick Lake 



Figure 1. — Hill southeast of Emerick Lake, Upper Merced Basin, Sierra Nevada. 

 The hill, which is about 250 feet high, is the terminal and culmi- 

 nating point of a long ridge of granite. The dome structure in 

 the ridge is anticlinal, changing in the hill to the inverted canoe 

 form. At the extreme right the convex or anticlinal curvature 

 is seen to merge into a concave or synclinal curvature, better 

 shown in figure 2. The hill was deeply buried by a glacier mov- 

 ing from left to right. Glacial erosion made the rock basin occu- 

 pied by the lake and excavated the hillside so as to expose the 

 dome structure in partial section. 



Figure 2. — A Syncline in dome structure. 



Emerick lake (figure 1) lies out of sight, just beyond the granite 

 slope at right. Its outlet, crossing the sill without notable incis- 

 ion, descends to the foreground at left. Structure and topo- 

 graphic configuration are in harmony. A syncline pitches toward 

 the foreground and also (slightly) toward the lake. At the lip 

 of the lake basin the cross -section is synclinal and the longitudinal 

 section anticlinal. 



Plate 4. — Joint Structure and Fire Spoiling 



Figure 1. — Jointed granite in Kuna Crest, Sierra Nevada. 



The granite is traversed by four systems of parallel plane joints. 

 The cliff is at the head of a glacial cirque, and the sloping plain 

 above it belongs to preglacial topography. The general forms of 

 cirque and plain are independent of the attitudes of the joint 

 systems. Compare with plate 3 and observe the contrast between 

 joint structure and dome structure. 



Figure 2. — Granite boulder from which spalls or flakes have been riven by the 

 heat of forest or meadow fires. 

 The spall at the left, still standing in position, illustrates the ap- 

 proximate parallelism of fractures thus produced to the exterior 

 surface. Probably in this case the strong heating was at the side 

 and local — as the heating would be, for example, if the log at the 

 right should be burned — and the small size of the spall was de- 

 termined bv the localization of the heat. 





