ENDLICH ON EROSION IN COLOEADO. 845 



worn ravines and gullies. This species of formation is greatly facilitated 

 by the action of pluvial erosion. Eain beating against walls, wbicli 

 have at certain places been prepared for its transporting force, can 

 readily carry away such portions that the isolation of columns will be 

 accomplished. After the column is once formed, erosion by sand driven 

 before the wind will hove a very appreciable effect upon the detail 

 ornamentation and sculpturing of its exterior. From the illustration 

 above referred to may be recognized more clearly what has here been said. 

 Scarcely any one monument can be found which does not show either 

 completed accessories, or such in the course of formation. In intimate 

 relation to the distribution of bowlders within the faces of the walls, is 

 the grouping of future monuments. How slowly or how rapidly they 

 may be formed, however, cannot even be surmised. 



In the course of time, the supporting column can no longer sustain the 

 weight of the capping stone and this drops off. This result is hastened 

 by the decrease of the diameter of that portion which has been desig- 

 nated as the ^' neck ". Upon the removal of the cap, therefore, the former 

 monument presents the appearance of a tall, slender, more or less coni- 

 cal shaft. These forms I have termed "needles" in previous reports. 

 When the destruction of the monument has progressed so far, its 

 end is hastened. Eapidly the conglomeritic mass loses in height, 

 becomes more obtuse, and unless new obstacles present themselves to 

 arrest the progress of the truncation, the only remnant of the former 

 monument will be a small mound of irregular-shaped bowlders and sand. 

 On the other hand, if the original form was a high one or broad, it is 

 very probable that from the ruins of former beauty will rise new forms, 

 smaller in dimensions, but similar in construction. Throughout the 

 entire locality, observations were made with a view to determine as 

 accurately as possible the method of formation of these interesting pro- 

 ducts of erosion. They have led to the results above enumerated, and, 

 although much more might be said with regard thereto, but little could 

 be added tending to throw further applicable light upon the subject. 



After ages have passed, the features for which this region may now 

 justly be called unique will have disappeared. The sure hand of erosion 

 will gradually cut down what even today are but the remnants of a 

 former extensive deposit. It is possible that the removal of soil and the 

 trachytes overlying the conglomerate may expose fresh surfaces to 

 attacks by erosion, and that thus the forms may be perpetuated. I am 

 acquainted with no locality which presents monuments that can appro- 

 priately be compared to those of South Eiver. Perhaps the nearest 

 approximation in form thereto may be found in the Tyrol, near Bozen. 

 They are composed of different material, however, but their genesis is 

 essentially the same.* At no place in Colorado certainly do we find so 

 complete a series of such forms, and one so advantageously situated as 

 to surroundings. 



* Compare Lyell, Principles of Geology, vol. i, p. 336. 



