556 N. H. DARTON FISH REMAINS IN ORDOVICIAN ROCKS 



Hills uplift has not been ascertained. Possibly there is a general thinning 

 of all the strata, but it is probable that there is simply a beveling off by 

 pre-Carboniferous erosion, so that the lowest layer extends farthest south. 

 Whether the formation was originally deposited in the southern Black 

 Hills region and subsequently removed by erosion or whether its absence 

 is wholly due to non-deposition is not ascertained. In its upper and lower 

 contacts the only evidence of unconformity which the formation presents 

 is the abrupt change of materials. In the Deadwood region there is, at its 

 top, a small thickness of greenish shales in which no fossils have been 

 found. These shales give place abruptly to the basal limestone (Engle- 

 wood formation) of the Pennsylvania division of the Carboniferous (see 

 figure 2, plate 77). The Whitewood limestone lies unconformably on the 

 Middle Cambrian, overlapping to the south and west onto lower beds than 

 those on which it lies near Deadwood. 



Absence of Ordovician in Laramie Mountains 



No evidence of the existence of Ordovician rocks is presented in any 

 portion of the Laramie mountains, including also the Casper and as- 

 sociated ranges. There are frequent exposures in which Carboniferous 

 rocks lie directly on the granites and schists, although in the northern 

 portion of the district there is an intervening sandstone which may be 

 either Carboniferous, Cambrian, or even Ordovician. No fossils were 

 found, but from its character and relations it is supposed to be Carbon- 

 iferous, probably Pennsylvanian. 



Absence of Ordovician in Hartville Uplift 



In the Hartville uplift lying between the Laramie range and the Black 

 hills the limestones of the Mississippian division of the Carboniferous lie 

 on Algonkian rocks, and Ordovician, as well as Silurian, Devonian, and 

 Cambrian, are absent. 



Ordovician in Eastern Colorado 



GENERAL EXTENT AND RELATIONS 



Along the east slope of the Eocky mountains there is a nearly general 

 overlap of Upper Carboniferous deposits onto the pre-Cambrian rocks, 

 but a few small areas of earlier Paleozoic rocks appear. These areas are in 

 the embayments west of Colorado Springs, west and north of Canyon City, 

 and in Perry park. The Ordovician rocks exposed consist of limestones 

 and sandstones usually lying on a thin mass of Cambrian sandstone, or 



