Poyue, Jr. — Geology and Structure of Volcanic Bocks. 231 



can hardly have the same underground relations. If those, 

 too, represent the edges of beds, and consequently expose their 

 cross-section, the abrupt endings of such formations and the 

 great stoutness of many of the lenses are difficult features to 

 explain. Besides, the predominance of horizontal bedding 

 near such formations is quite incompatible with such an idea. 

 A satisfactory explanation lies in the consideration of these areas 

 as occurring on the crests of great folds. This position allows 

 of a most irregular surface slope, with abrupt endings against 

 other formations, when planation has exposed a particular bed 

 to view ; and is, moreover, in accord with existing bedding 

 planes. 



3. The relation between schistose and massive formations 

 throws further light on the structure. Schistosity is not 

 developed alike in all parts of the area ; it appears to have 

 been the result of a selective action, so that some belts are 

 predominantly massive, whereas others are strongly schistose. 

 This cannot be explained by a difference in the nature of the 

 formations ; for the same formation may in one place be 

 massive, and in another, badly mashed. • The position of a 

 rock mass, therefore, is apparently a much more important 

 factor in determining its degree of schistosity than its litbo- 

 logic character. It follows, accordingly, that, although the 

 region as a unit was subject to compression, some portions 

 were so situated as to escape any important effects of such a 

 force. The crests of folds would afford positions favorable for 

 the transmission of a great compressive force without impor- 

 tant molecular adjustments ; the limbs would involve a greater 

 slipping between beds and consequently be susceptible to the 

 greatest degree of mashing. This assumption best fits the 

 facts observed. 



The three lines of evidence concur, then, in making pretty 

 conclusive proof that the region is folded. The exact nature 

 of the folding is a more difficult thing to determine. Yet an 

 application of the same three principles indicates that the 

 region very probably represents in general two anticlines and 

 one syncline, the axes of which extend in a northeast direction 

 in agreement with the schistosity. Flat Swamp Ridge is con- 

 sidered the trough of the syncline ; and the two corresponding 

 anticlines are near the northeast and southwest borders, 

 respectively, of the district. 



Consequent upon the major folding, a series of subordinate 

 crumplings and crinklings were of necessity formed ; but these 

 have been so obscured by weathering and other changes 

 as to baffle detection. Their presence is only indicated by 

 an occasional bedding plane out of accord with other measure- 

 ments in its vicinity. 



