Domes and Dome Structure. 



213 



curvature are always adjusted to the general shapes of the 

 topography. In the last respect they differ greatly from the 

 structures produced by folding of strata. The curves of 

 folded strata are diversely related to topographic features. 

 A syncline may be found in a valley or on a hilltop, and an 

 anticline may have either of these positions ; but in dome 

 structure each anticline coincides with a summit and each 

 syncline with a valley. If the dome structure were origi- 

 nal, we should expect that it would often be traversed 

 discordantly by superposed drainage and dissection, and 

 the fact of its accordance with features of dissection is 

 therefore imfavorable to the theory that it is an original 

 structure. 



Where the granite is divided by a solitary joint into 

 distinct masses, the dome structure of each mass is inde- 

 pendent of the structure developed in its neighbor (figure 

 i). The curves of the dome structure do not cross the 

 joint plane, and are thus shown to be newer than the joint. 

 This phenomenon is not favorable to the view that the 

 structure is original. 



These considerations, as they were developed gradually 

 in the field, led me to abandon altogether the hypothesis 

 that the structure was developed either in the original con- 

 stitution of the granite or at some early stage in its history, 

 and to adopt the alternative view that it followed the pro- 

 duction of the principal topographic features and was in 

 some way conditioned by the surface forms. 



Relation of Dome Structure to Plane Jointing. — The 

 dome structure appears to have been developed only in 

 massive rock ; that is to say, it is not found in rock which 

 is divided by systems of parallel plane joints. Through 



