DOME STRUCTURE IN CONGLOMERATE 565 
It is worthy of note that domes are so far known to occur only in 
plutonic rocks or in a clastic rock made up entirely of material of 
plutonic origin. This is true probably because the coincidence of 
texture and mineral constitution, essential to the peculiar type of 
weathering causing the scaling process, is confined to plutonic rocks. 
SUMMARY OF OBSERVATIONS 
Concerning the scaling process itself in the conglomerate the fol- 
Fic. 5.—Dome surface in conglomerate at western end of Eagle Rock Valley, 
viewed from the south, showing crevice under large scale. 
lowing observed facts and the deductions drawn from some of them 
may be given: 
1. The scales are not found on slopes of less than 30° or 40°, thus 
showing that the process is influenced by gravity. 
2. The scales are almost entirely absent from the exposed southern 
faces and other portions of the rock, which are kept dry or practically 
dry, most of the time, indicating that moisture is a necessary agent 
in the process. The paucity of the scales on the surfaces most exposed 
to the sun argues against change in temperature being responsible for 
their formation. 
