840 BULLETIN UNITED STATES GEOLOGICAL SURVEY. 



erosion by frost, these fissures allowed considerable quantities of the 

 shale to drop off on account of the pressure produced by the cap-stone. 

 Dependent upon the direction and extent of the fractures is the trans- 

 verse section of the column. If they are continuous, and mainly trend 

 in one direction, it will be elliptic. If not continuous, and running in 

 several directions, the shaft will more probably have a round cross- 

 section. Frost and pressure, then, may be regarded as the chief agents 

 in determining, in this instance, the form of the column. Sand will have 

 but little direct effect upon shales, as they do not offer resistance suf- 

 ficiently' great to produce direct fracture. 



In the course of time, the supporting column of shale becomes so thin 

 that it can no longer sustain the weight of the cap. It is crushed, and 

 soon nothing remains to mark the former monument but a small mound 

 of arenaceous clay. The duration of products of erosion like these on 

 Douglas's Creek must necessarily be shorter than that shown by the 

 analogous forms of Monument Park. Not uufrequently very small ones 

 may be found, but I have nowhere seen any comparable in size to those 

 iust described. In a region so monotonous as regards scenery as the 

 one south of White Eiver, even a slight variation from the typical bluff 

 and rocky wall produces a pleasing impression. Though the rocks there 

 afford auiple opportunity for the formation of such groups, their perish- 

 able nature probably accounts for the rarity of the occurrence. 



ACCIDENTAL MONUMENTS. 



As accidental monuments I designate such having a different genesis 

 from those described above. Whereas the former represent a certain 

 unbroken portion of one specific geognostic group, these latter are com- 

 posed of members of two groups mainly. Thus the conglomerate, cap- 

 ping the monuments of the Garden of the Gods, is the next youngest 

 product of deposition to the neck of the column. In accidental monu- 

 ments, however, no such relation exists. I have considered it advisable 

 to make this distinction, as the very classification conveys a certain 

 amount of information. We have, in Colorado, numerous representa- 

 tives of both types, and have had occasion to study both of them 

 thoroughly. As will be seen, the monuments of this class may lay claim 

 to greater grandeur than the preceding ones. Less accessible, as to 

 location, than the latter, they will probably remain unvisited for many 

 years, until the energetic tourist may finally conquer all obstacles and 

 disturb their present seclusion. 



SOUTH RIVER. 



South Eiver heads on the continental divide about west longitude 107° 

 and north latitude 37° 34', and flows in a northerly direction. After a 

 course about 10 miles in length, ic enters the Rio Grande del Norte, a 

 tew miles below Antelope Park. Eising near South Eiver Mountain, 



