Apeil 16, 1897.] 



SCIENCE. 



605 



along tlie southwest side of the narrow 

 Manitou Park, basin of sedimentary rocks 

 (Silurian and Carboniferous) . Among the 

 more important characteristics of the dikes 

 noted by Cross are the following : 1. The 

 dikes have a general trend parallel to the 

 belt in which they occur ; are approximately 

 vertical and often appear as a complex of 

 nearly parallel fissures with many branches 

 and connecting arms; and vary in width 

 from mere films to two or three hundred 

 yards, the largest being a mile or more in 

 length, and forming rugged ridges with nar- 

 row crests which contrast markedly with 

 the gentle sloping hills of granite about 

 them. In short, " In all formal relation- 

 ships to the enclosing rocks these bodies are 

 as typical dikes as any of igneous origin." 

 2. The rock of the dikes is a fine and 

 even-grained aggregate of sand grains vary- 

 ing in degree of induration from a normal 

 sandstone to a dense hard quartzite, but 

 throughout of a remarkably massive and 

 uniform character. 



During the past summer of 1896 I was 

 able to devote several weeks to the investi- 

 gation of the sandstone dikes and the great 

 displacement to which I have found them 

 to be genetically related. To the dikes de- 

 scribed by Cross I gave only sufficient at- 

 tention to become familiar with their char- 

 acteristics, and then endeavored to trace 

 the series southeastward through Ute Pass 

 to Manitou and beyond. 



The sedimentary formations of the Mani- 

 tou area embrace, from below upward, as 

 described by Hay den, Cross and others : 

 1. A basal sandstone which is usually 40 to 

 50 feet thick, white or gray for the lower 

 10 to 15 feet and dull red or brown above, 

 only rarely of arkose character, but fre- 

 quently more or less glauconitic. 2. This 

 sandstone, which may be referred provi- 

 sionally to the Potsdam, becomes calcareous 

 upward, passing into red, cherty limestones, 

 and these into a massive gray limestone 



having a thickness of several hundred feet. 

 The limestones are throughout more or less 

 magnesian and contain recognizable traces 

 of a Lower Silurian (Ordovician) fauna. 

 3. This great Manitou limestone series is 

 overlain without apparent unconformity by 

 the Fountain (Carboniferous) beds 1,000 to 

 possibly 1,500 feet in thickness — a remark- 

 able complex of red and white arkose sand- 

 stone, grits and conglomerates. 4. The red 

 sandstone series (Triassic), a thousand feet 

 or more in thickness. 5. The white, varie- 

 gated and gypsiferous Jurassic strata. 6. 

 The Cretaceous series, beginning with the 

 massive and conspicuous Dakota sandstone. 

 Each of these formations is cut off on the 

 south by the great fault which skirts the 

 northeastern base of the Pike's Peak mas- 

 sif. This profound displacement, which 

 must be regarded as a dominant factor in 

 the geological structure of the region, and 

 to which we undoubtedly owe, in the main, 

 the Manitou embayment of sedimentary 

 rocks and the exceptional elevation of the 

 Pike's Peak massif as compared with the 

 Front Kange to the north of Ute Pass, 

 gained early recognition and is clearly in- 

 dicated on Hayden's maps of the Manitou 

 area. It is altogether probable that the 

 fault by which Cross has bounded the Mani- 

 tou Park sediments (Potsdam, Manitou 

 limestone, and Fountain series) on the 

 southwest is a direct continuation of that 

 which, cutting across the strike of the beds, 

 is so much more conspicious in the Mani- 

 tou area. This great displacement, which 

 divides very obliquely the entire Front 

 Range and the beds lying upon either flank 

 of the range and sloping away from its 

 crest, may therefore be appropriately 

 designated the Ute fault. Erosion has cut 

 deeply enough over the top of the arch to 

 remove the sedimentary rocks from the 

 down-throw as well as the up-throw side of 

 the fault. The Ute fault cuts every forma- 

 tion of the region from the fundamental 



