212 CARBONIFEROUS KOKMATKINS AND KAirNAS OF COLoKADO. 



caulioii. because enough is known to raise many (|uesti(jns in i-egard to it, hut too 

 little to answer them. 



In the interior tliere is only the inconsiderabh! thiclcness of the Yule limestone, 

 with perhaps the Parting quartzite, by whieh it seems possible that only a small 

 portion of Ordovician time can be represented. In the Pikes Peai<: (juadrangle Cross 

 lias diserimiuated the Manitou limestone, the Harding sandstone, and the Fremont 

 limestone, all of Ordovician age. The faunas of the Harding and Fremont are those 

 of the upper Ordovician (Trenton), and I doubt if the lowest Ordovician is repre- 

 sented. Another gap would then exist between the highest Cambrian and the lowest 

 Ordo^■ician ])ed. Cross notes an unconformity of overlap between the Harding sand- 

 stone, and I can not believe that this unconformity, or the movements which caused 

 it, were restricted to the immediate region of the Pikes Peak quadrangle. It can 

 probably safely be said of the Ordovician that it is now represented by fragments, 

 and that deposition was affected (and possibly the present existence governed) by 

 contemporaneous movements. The Upper Silurian appears to be entirely wanting 

 in Colorado, and most of the Devonian as well. The latter period is very doubtfully 

 represented by^ the Parting quartzite, whose age is not detinitel}' known, and certainly 

 by the lower part of the Ouray and Leadville limestones, whose fauna belongs to the 

 upper Devonian. No rocks were formed, then, from the end of Ordovician to 

 toward the end of Devonian time, or if formed they were also swept away again. 

 The upper portion of ,the Ouraj^ and Leadville limestones carries a Mississippian 

 fauna, and while the faunal break is what one might almost call absolute, the litho- 

 logical indications are that sedimentation was continuous from the Devonian. But 

 the sharp faunal break and the fact that apparently in places, as along the Front Range 

 the upper limestone with the Mississippian fauna exists without the lower, would 

 seem here again to indicate an overlap and jjossibly an interval of erosion or non- 

 deposition. The upper portion of the Ouray and Leadville limestones is of Missis- 

 sippian age. Its upper limit is marked by an erosional unconformit}*, and the paleon- 

 tological evidence indicates that only lower Mississippian time is represented. The 

 middle (?) and upper Mississippian, and probablj" part of the Pennsylvanian, are 

 wanting through ei'osion or nondeposition. The lower part of the Hermosa (and the 

 Molas formation where present), which succeeds the Ouraj-, I am disposed to correlate 

 with the Weber shale and the Weber limestone, which foUoAV the Leadville limestone. 

 Their deposition appears to have been consecutive with that of the rest of the Hermosa 

 and with the lower Maroon and the Weber grits, which I also correlate. At the same 

 time the Maroon sediments transgress the Weber series, and in fact all the earlier 

 Paleozoics, and in the Crested Butte quadrangle and elsewhere lap over upon the 

 Archean. There is also a certain individuality about the lower Hermosa and the 

 Weber faunas, while the conglomerates of the lower Maroon contain pebbles of 



