646 



DYNAMICAL GEOLOGY. 



Anticlinal strata give rise to another series of forms, in part the reverse of the pre- 

 ceding, and equally varied. Figs. 1088-1C91 represent some of the simpler cases. 



1082 



Figs. 1082-1 ( 



When the back of an anticlinal mountain is divided (as in Figs. 1088-1090), the moun- 

 tain loses the anticlinal feature ; and the parts are simply monoclinal ridges. As the 



Fiffs. 1088-1091. 



1088 



Fig. 1092. 



anticlinal, in the progress of its formatipn, is almost sure to have its back fractured, 

 from the strain on the bending rocks, the removal of the upper and central portion, 

 making a broad valley in its place, is the common fact. 



In Fig. 1091, the anticlinal character is distinct in the central portion, while lost in the 

 parts either side. To the right, in this figure, is shown a common effect of the protection 

 afforded to softer layers by even a vertical layer of hard rock :* the vertical layer forms 

 the axis of a low ridge. 



Fig. 1092 represents some remarkably slender columns of Tertiary sandstone, from 



the Report of Dr. Hayden for 1873. There 

 are here two layers harder than the rest; 

 and one has been left to make the top of 

 the taller column, while another caps a 

 shorter series. These examples of nature's 

 modelling are very numerous in Colo- 

 rado, over what has been called Monument 

 Park. The erosion is due to the rains, or 

 the rills they produce, and the later part 

 to the gentler action of rain-drops, together 

 with the action of the winds and frosts. 

 Lyell has described a remarkable example 

 of erosion by rains, of a thick deposit of 

 reddish indurated mud, containing scat- 

 tered bowlders, really a moraine, occurring 

 near Botzen in the Tyrol, in which the re- 

 sult is a region of many hundreds of slen- 

 der pillars and columns of half consolidated 

 earth, twenty to a hundred feet in height, 

 and each capped with a bowlder, — some 

 of the stones two or three feel in diameter. 

 He gives a view of one such scene in his 

 Erosion, Monument Park, Colorado. "Principles," chapter xv. 



The above are the simple results from the erosion of folded rocks. They serve as a 

 key to the complexities of features common through a large part of the Appalachians 

 and other regions of folded rocks, where synclinal and anticlinal axes are in numberless 

 complicated combinations, rendered doubly puzzling by faults. See, further, pages 

 93-98. 



