564 RALPH ARNOLD 
Eagle Rock. Some of these are little more than huge boulders, and 
one of them is only about ten feet in diameter. This last one, however, 
presents a very characteristic dome surface, with accompanying 
scales and arches on three sides, east, north, and west. In the vicinity 
of the small dome is the conglomerate exposure shown in Fig. 5. 
Taken as a whole it is but a small frac- 
tion of a complete dome, but it offers the 
best opportunity for detailed study of the 
phenomena of dome formation of any of 
the examples in this region. The view is 
looking north; the conglomerate dipping 
northeast. The surface bows over from 
a slope of 30° to one of approximately 
60°. ‘The overhanging block on the face 
of the dome is about four feet thick at its 
thickest point, and consists of hard, little- 
weathered conglomerate. The block 
thins toward the southeast (the right in 
the photograph), the crack under it nar- 
rowing proportionately at the same time. 
Fic. 4.—Profile of north 
face of Eagle Rock, with detail 
of scale at S, latter showing 
transverse crack in scale. In direct contrast to this hard sheet is 
a 3-foot zone of weathered rock shown in 
detail in Fig. 6, which was taken looking west into the crack extend- 
ing under the, outer shell on the; leit. in Pig! 5. lhe hammer 
stands vertical, the handle resting on the hard surface of the new 
dome face, the head resting against the weathered zone, and the 
upper portion of the picture displaying the hard outer shell. The 
weathering process has resulted in the formation of a series of laminae 
(noticeable in the picture above the head of the hammer), from a 
small fraction of an inch to an inch in thickness extending approxi- 
mately parallel to the dome surface. The planes separating the 
laminae pass through the conglomerate in most cases irrespective of 
the composition and hardness of the component parts of the rock, 
appearing to cut the hard granitic cobbles as readily as the softer 
arkose matrix. An exception to this is the exceedingly hard aplite 
boulder seen on the extreme left of the photograph. An idealized 
profile of the dome-face just described is shown in Fig. 7. 
