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Sierra Club Bulletin 



flowed over a region of domes, the superior strength of their 

 concentric structure has prevented them from being so exten- 

 sively denuded as the weaker forms in which they He imbedded ; 

 but after thus obtaining a considerable elevation above the gen- 

 eral level, unless their cleavage planes were wholly latent they 

 were liable to give way on the lower side, producing forms like 

 Fig. 8, in every stage of destruction. In the case of rocks 

 wherein no cleavages of any kind were developed, forms have 

 resulted which express the greatest strength considered with 

 reference to the weight and direction of the glacier that over- 

 flowed them. Their most common form is given in Fig. 9. 

 Some of their cross-sections are approximately given in Fig. 

 10. But few examples are to be found where cleavage and 

 irregularity of hardness do not come in to complicate the prob- 

 lem, in the production of that variety of which nature is so 

 fond. 



We have already seen that domes of¥er no absolute barrier 

 to the passage of vertical and horizontal cleavage planes ; but 

 it is also true that domes cut one another. Fig. 11 is a section 



Fig. II. centric layers of a dome, 



marked thus present themselves on the overleaning wall of 

 the gorge, and upon the buried dome whose section thus ap- 

 pears another dome is resting, furnishing conclusive evidence 



