ENDLICH ON EROSION IN COLORADO. 849 



ing the bust and head of a most venerable-looking, bald-headed man. 

 Changing slightly our course, the spectacles of the old man turned into 

 the shield of a cap, his bald head grew elongated and was onamented by 

 a round button on top ; his nose grew longer 5 the chin retreated and 

 with it the prominent breast, while a corresponding curvature of the 

 upper portions of the spine took place. We had, instead of an eminent- 

 looking man, a typical representation of the race-course. Not long, 

 however, did this figure last, for a short turn, shortly after, revealed to 

 us the characteristic features and head of a negro baby. Numerous 

 such instances could be described from that locality, instances where 

 the most absurd caricatures were seen on a gigantic scale. 



I have selected for illustration in the Annual Rei)ort for 1876 a small 

 group within the caQon of White Eiver at the junction of a small stream 

 therewith. Three isolated columns, approximately round upon cross- 

 section, occupy the summit of a small, smooth hill. The highest one is 

 about 80 feet high. A little behind it stands one less regular in outline, 

 and to one side is the smallest, very thin shaft. Struck by the appro- 

 priate and almost affectionate disposition of the group, we at once 

 designated the figures as the " Happy Family ". Quietly and in harmony 

 they have thus stood side by side for centuries, probably, and they well 

 merit recognition at the hands of explorers. 



The first essential structural condition of rocks exhibiting such 

 features is the lack of homogeneousness. Differences of texture must 

 occur, not along the planes of bedding, but irregularly distributed 

 throughout the mass. In order that this may be accomplished, it is 

 necessary that the rock should not be separated into thin strata or lay- 

 ers, but should form thick, heavy masses. In that case, the percolation 

 of mineralized waters and the action of other agents producing chemical 

 changes can result in a thorough disturbance of a uniform constitu- 

 tion. Within the White Eiver region we find that the Upper Green 

 Eiver sandstones contain irregular admixtures of cementing material, 

 thus rendering them, firstly, of unequal hardness, and, secondly, pro- 

 ducing unequal resistance to eroding agents. This condition is a neces- 

 sary one for the occurrence of forms such as have been described. Were 

 it not for this textural inequality, the processes of abrasion and decom- 

 Ijosition must simply take place in accordance with the climatal condi- 

 tions of the country and the composition of the Sandstones, without 

 producing the results observed. In this instance, however, portions 

 that are constantly exposed to atmospheric influences, more so than 

 others, have been able to withstand them by virtue of these physical 

 variations. 



Fluviatile erosion gave the first direction as to the distribution of 

 monumental and other forms. Evidence there obtained tends to show 

 that extensive transverse fractures — -joints — more or less open must have 

 traversed the sandstones. These were undoubtedly taken advantage of 

 by the flowing waters. While on the one band they facilitated the exten- 



