ESDLicH.] GEOLOGY SAN LUIS DISTEICT, SECTION A. 313 



in age to Carbouiferous, progressing from old to younger, we find in sec- 

 tion a a series of beds that I combine under the term Mesozoic. 



It remains to be stated that in the subsequent pages this word is used 

 to denote a formation, or a series of formations, younger than the Per- 

 mian, older than the Cretaceous; so that its age will rank with that of 

 the Triassic and Jurassic. Although strata that must be referred to 

 this group cover a large extent of ground throughout Colorado, the pale- 

 ontological evidence that has been furnished, by which its relative age 

 might be determined, is very scant — too scant altogether to admit of 

 any thorough or strict identification, and it is necessary therefore to 

 assign to them the position indicated with some reserve. 



Interrupted at a number of i)laces, this formation is found all along 

 the eastern slope of the Front range in section a. Following up Oil 

 Creek, we find that a bay existed there as late as the Cretaceous period, 

 and the Mesozoic beds are exposed at a number of points. West of 

 Canyon City the same beds are exposed, but do not extend into the Cre- 

 taceous bay that there runs parallel to the Arkansas Eiver. The strata 

 composing the lower portion of this series are usually termed the " red 

 beds," and form more or less steep blufis, standing out boldly from the 

 underlying granite, and frequently weathering in grotesque groups. 

 Although not so strikingly picturesque as the Garden of the Gods near 

 Colorado City, farther south of that locality a number of small "gardens" 

 may be seen that owe their singular scenery to the presence of these 

 red beds. 



Beginning at the north end of the Front range, as far as it is inclosed 

 by the limits of section a, and traveling southward, the average thick- 

 ness of these beds is found to undergo but comparatively slight changes. 

 A series of sections comiDaring the succession of formations was taken 

 along several points of the eastern border of the range. The first one 

 runs through station 97., the second at station 96, the third a short dis- 

 tance west of Canyon City through station 11. All these have been 

 taken at right angles to the local trend of the range, thus varying from 

 east to south in direction. First examining the section through station 

 97, (Plate X, section A,) we find coarse-grained red sandstone resting 

 immediately upon the granite, dipping at an angle of 18° to 20° to the 

 southeast. Throughout the entire section, the angle of the dip decreases 

 as the distance between the point of observation and the junction with 

 the granite increases; therefore, no further mention will be made of it. 

 The sandstone just mentioned is covered by a stratum of white, also 

 coarse-grained, sandstone, which in turn underlies red. Upon this is 

 deposited a stratum that presents a good, well-defined horizon throughout 

 section a ; it is the coarse-grained red conglomerate, (c,) varying some- 

 what in thickness. It may be observed that toward Canyon it gradually 

 increases. Small bowlders are its component parts, usually well rounded, 

 quartzitic in character, but not sufficiently well identified to assign them 

 to any one of the observed formations as their original place of deposi- 

 tion. Argillaceous material cements them, and it can be said that from 

 the character of the single fragments found it may be inferred that 

 they formerly belonged to- some stratum or strata deposited by mechan- 

 ical action. A series of red shales {d) cover, this conglomerate, very 

 sandy in places, so that they might almost be considered as highly argil- 

 laceous sandstones, easily yielding to atmospheric influences. Thick 

 strata of red sandstone follow, overlaid by white and yellowish shales, (e,) 

 partly dolomitic, interstratitied with banks of limestone. Eising up 

 from these beds in a characteristic bluff is a yellow sandstone, (/,) some- 

 times shading over into brown, lied sandstone overlies, and these two 

 together probably form Cretaceous No. 1. White shales and limestones 



