586 A. W. GRABAU TYPES OF SEDIMENTARY OVERLAP 



Tenmile districts, at Leadville, and elsewhere. At Manitou park 100 feet 

 of sands lie between the fossiliferous Ordovicic limestones and the 

 granite. In the upper bed of this sandstone series Lingulepis and Obohis 

 have been found, on the strength of which discovery these sandstones are 

 referred to the Cambric. At another point in the Park the thickness of 

 this series is 86 feet, while in still another section 40 feet of sandstone 

 intervene between the granite and the Ordovic limestone. 



The section at Perry park was examined by the writer. On the granite 

 lie about 100 feet of sandstones, with some cherty limestones, followed 

 by a thin bed of brecciated rock in which the fragments are limestone and 

 chert. This is immediately succeeded by a cherty limestone carrying 

 Carbonic fossils and referable to the Milsap limestone of Cross. The 

 brecciated bed may indicate a line of disconformity, which would justify 

 the reference of the basal sands to the Upper Cambric. On the other 

 hand, the bed referred to shows no evidence of so extensive an erosion 

 interval as would be necessary to make the basal bed Cambric. There 

 seems to be no valid reason why we should not return to the earlier view, 

 namely, that these basal beds are also Carbonic, resting by overlap 

 directly upon the granite. If this is the case, this sandstone is probably 

 not continuous with the basal sandstone of Manitou, the overlap being of 

 the irregular instead of the progressive type. 



Another section was examined by the writer in Williams canyon, near 

 Manitou Springs, and a detailed analysis of the beds was made. The 

 basal portion was also examined in Queens canyon. In both cases lime- 

 stones with Ordovicic fossils were found a short distance above the basal 

 sandstone, of which there are 48 feet in Williams canyon and less than 

 half that amount in Queens canyon. At Canyon City, Walcott found the 

 Harding sandstone resting unconformably on the Algonkian gneiss and 

 miscaceous schist. The base is a 5-foot bed of coarse light gray sand- 

 stone, followed by sandstones becoming gradually more reddish and 

 purplish and containing a Lower Trenton molluscan fauna. With these 

 occurs the remarkable fish fauna characteristic of this formation.* Else- 

 where in this region, however, Lower Ordovicic limestones and basal sand- 

 stones referred to the Cambric occur below the Harding. 



The basal sandstones of the Front range, except in such cases as the 

 Harding sandstone, are generally regarded as of Upper Cambric age. 

 That some of these sandstones are of later age than Cambric, representing 

 the continuous encroachment of the sea into Ordovicic time, can hardly be 

 questioned. In fact, from the character of the few fossils found in the 

 limestones immediately overlying, there is some reason to believe that in 



* Walcott : Bull. Geol. Soc. Am., vol. 3, 1892, pp. 153-172. 



