56 GEOLOGICAL SURVEY OF THE TERRITORIES. 



remarkable upthrusts of igneous material, vertically through the over- 

 lying sedimentary beds. The Cretaceous strata of Nos. 3 and 4 extend 

 up on the sides of the peak about 1,000 feet above the bed of East 

 Eiver, with very little inclination, and between the strata of shale were 

 pressed out portions of the igneous material. 



The illustration, Plate XI V,4s'so clear that but little space need be 

 used in explanations. The shale all belongs to Cretaceous formation 

 No. 4. An examination of the map and plate of sections would indicate 

 that the aggregate force which elevated the Elk range acted vertically 

 with a tangential movement or shove, as it were, from the northeast toward 

 the southwest. There are many faults of remarkable character on the 

 northeast side of the axis, but no very marked examples of the inversion 

 of strata, but on the southwest side of the axis this feature is shown in 

 a marked degree. Time will not permit us to work out in detail in this 

 report the wonderful complications in the strata, which have been pro- 

 duced by the various elevating forces in this range. Much of it was 

 brought out in the various reports in the annual report of the survey 

 for 1873. Mr. Holmes will also introduce important details into his 

 report. I shall, therefore, at this time, confine myself to a general view 

 of the geology of this range, which, with the beautiful and remarkably 

 clefar illustrations, will be sufficient for the information of the geologist. 



The axis of the Elk range can be easily traced on the map, and the 

 axialsection will show the immense masses of strata that were carried 

 high up to the very summits of the range. 



At the southeast corner of the map it will be observed there is a con- 

 siderable area designated as metamorphic granite. This forms a part 

 of the Sawatch Mountains, and may serve to show the relations of that 

 range. To the west of it there are narrow belts, marked as Silurian 

 and Carboniferous. These represent masses of strata that were origi- 

 nally lifted up by the Sawatch range and incline toward the west. On 

 the completed geological map of Colorado, the connection of these 

 fragmentary masses of sedimentary strata about the summits of the high 

 granite mountains will be made clear. We shall hereafter attempt to 

 show by a series of sections, not only that the Triassic, Jurassic, and 

 Cretaceous groups originally existed here in full force, but that they 

 probably extended across the area now occupied by the Sawatch range 

 and were united with the sedimentary beds of the South Park range. 



The northeastern slope of the Elk group slopes down into the valley 

 of the Eoaring Pork, an important branch of Grand Eiver. Here we 

 find a large area of the various divisious of the Cretaceous group. The 

 Dakota group rests upon the Jurassic, but is not exposed to any great 

 extent, except in the canons or gorges of the streams. So far, therefore, 

 as a map is concerned, it cannot be represented except by a very nar- 

 row band, but above it there is from 1,000 to 1,500 feet of the remaining 

 portions of the group, Nos. 2, 3, 4, and 5, but not as well defined even 

 as on the eastern side of the Colorado or Front range. The greater 

 portion is composed of black shaly clays with thick beds of sandstones 

 appearing in different positions. A few Cretaceous fossils occur, of well- 

 known and common genera, as Ammonites, Baculites, and Inoceramus. 

 Very few of the smaller forms were observed. This singular Creta- 

 ceous area seems now to form a sort of basin with the Jurassic and 

 Triassic, or Eed Beds all around it. Its peculiar form will be noticed 

 on the map. The Cretaceous beds occupy very varied positions, 

 sometimes high up on the mountain -sides nearly to the summits, 

 and then filling up the lower valleys. The faults are without num- 

 ber, for in the process of elevation the strata seem to have been 



