NOTE ON SOME PECULIAR FORMS OF EROSION IN EASTERN 

 COLORADO, WITH HELIOTYPE ILLUSTRATIONS. 



By F. V. Hayuen. 



The two plates, VII and YIII, to which the attcDtiou is directed in this 

 brief note, have been printed by the heliotype process of J. K. Osgood & 

 Co., of Boston, Mass., and are introduced in this connection as an experi- 

 ment. Necessarily, they present the accuracy, fidelity, and detail of the 

 original photograph, and on that account will be studied by geologists 

 with iuterest. They illustrate two distinct forms of erosion, the rock.' 

 belonging to widely different geological epochs. The jjower of tin 

 atmospheric agents in giving form to the surface-features in regard t 

 magnitude as well as variety, is nowhere more strikingly manifestet 

 than in Colorado. We hope from time to time to publish selectiont 

 from the more instructive of the scenic views, to illustrate these unique 

 forms of earth sculpture. 



In Plate VII, entitled "Picturesque pine and Castellated rocks,'' 

 are shown some most singular castellated sandstones, from forty to 

 sixty feet in height, located just south of the divide, near the head c ' 

 Monument Creek, within a short distance of the base of the mountains. 

 For a distance of about twenty-five miles in this region the sanl- 

 stones of the lignitic or Monument Creek group, jut up against the 

 granites of the mountain foot-hills with a comparatively slight in- 

 clination, varying from 5^ to 15°. For this distance, the sandstones lap 

 on to the granites, showing but little change in the elevation since their 

 deposition. They show clearly that the Colorado range had reached 

 nearly its present height prior to the deposition of the lignitic group. 

 All the rocks of older date are concealed, from a point south of Monu- 

 ment Creek north, across the " divide" to the south portion of the drain- 

 age of the South Platte. These isolated columns, of which there are only 

 a few, are very interesting, as remnants of beds that originally extended 

 over a large area, but have been removed by erosion. It is not at all prob- 

 able that they represent the original thickness of these beds; for in the 

 plains, some miles to the eastward of the base of the mountains, are nu- 

 merous high buttes, that would indicate that at least one thousand to fif- 

 teen hundred feet of the lignitic strata had been removed. Though dif- 

 fering much in form, these columns are of the same geological age with 

 those which occur in Monument Park, farther to the southward, and are 

 well shown in the annual report of the survey for 1873, page 32, Figures 

 4 and 5. The sediments vary much at different localities, being some- 

 times quite fine, of a yellowish cream-color, and again, a rather coarse 

 aggregate of small pebbles or grains of quartz, without much coherence. 

 The atmosphere acts with considerable ease on these rocks, carving them 

 into a great variety of forms. In the foreground we see a crooked pine- 

 tree, peculiar to this region, and at the right upper corner the sun shin- 

 ing through the leaves, or really the sun itself. The character of the sur- 

 rounding surface, with the peculiar vegetation, is also seen. The col- 

 umns present a kind of ribbed appearance in the picture. This is due 



