PHYSICAL FEATURES OF COLORADO VALLEY. 397 



Order 2. Longitudinal valleys, having a direction the same as the 

 strike. 



Of the first order, three varieties are noticed : 



a, dlacUnal, those which pass through a fold. (Fig. 3.) 



b, catacUnal^ valleys tliat run in the direction of the dip. (Fio-. 4.) 



c, anaclinal^ valleys that run against the dip of the beds. (Fig. 7.) 

 Of the second order, we have, also, three varieties : 



A^ anticlinal valleys, which follow anticlinal axes. (Fig. 5.) 



B, synclinal valleys, which follow synclinal axes. (Fig. 6.) 



C, nionoclinal valleys, which run in the direction of the strike be- 

 tween the axes of the fold one side of the valley formed of the sum- 

 mits of the beds, the other composed of the cut edges of the formation. 

 (Fig. 8.) 



Many of the valleys are thus simple in their relations to the folds ; 

 but, as we may have two systems of displacements, a valley may be- 

 long to one class, in relation to one fold, and to another in its relation 

 to a second. Such we designate as complex valleys. 



Again, a valley may belong to one class in one part of its course 

 and to another elsewhere in its course. Such we designate as com- 

 pound valleys. It will be further noticed that valleys may have many 

 branches, but, in relegating a valley to its class, we consider only the 

 stem of the valley proper, and not its branches. 



A great diversity in the features of all these valleys is observed. 

 Most of these modifications are due to three principal causes : First, 

 a greater or lesser inclination of the rocks. Second, the texture 

 of the beds that is, their greater or lesser degree of heterogeneity. 

 The third class of modifying influences is found in the eruptive 

 beds. 



The last-mentioned agencies are not found in the region underinmo- 

 diate discussion. 



The explanation of the caiions of Green River will assist us in un- 

 derstanding the origin of the lateral valleys and canons. The streams 

 were there before the mountains were made ; that is, the streams 

 carved out the valleys, and left the mountains. The direction of the 

 streams is indubitable evidence that the elevation of the fold was so 

 slow as not to divert the streams, although the total amount of eleva- 

 tion was many thousands of feet. Had the fold been lifted more 

 rapidly than the principal streams could have cut their channels, 

 Green River would have been turned about it, and all the smaller 

 streams and water-ways would have been cataclinal. 



Thus it is that the study of the structural characteristics of the 

 valleys and canons teaches us, in no obscure way, the relation between 

 the progress of upheaval and that of erosion and corrasion, showing 

 that these latter were^^aW passu with the former, and that the agen- 

 cies of Nature produce great results results no less than the carving 

 of a mountain-range out of a much larger block lifted from beneath 



