426 BibUograjjJiical Notice. 



This complete and careful organization has produced the excellent 

 results told in the valuable Tolurae before us ; and the carefulness 

 of this work, as well as the number and excellence of the illustra- 

 tions, reflects considerable credit on the department to whose energy 

 we are indebted for this valuable addition to scientific know- 

 ledge. 



Starting from Denver on the South Platte river, where the head- 

 quarters were established, the various divisions examined and 

 mapped that portion of the territory extending, roughly sjjeakiug, 

 from Xorth Park to rather further south than the valleys of the 

 Gunnison and Arkansas rivers, or between the 38° and 40^^ 30' 

 parallels of north latitude, and between the 105° and 108° meri- 

 dians of west longitude — thus comprising the mountainous dis- 

 trict of the North and South Park, Elk, Sa watch, and Colorado 

 frontier ranges. 



"This new area presented all the different forms of surface- 

 erosion peculiar to a granite, sedimentary, and lava countr}-, making 

 it an exceedingly interesting study, both for its topography and 

 geology. The great lava mesa at the head of the White Kiver is 

 cut by deep canons that penetrate far into the plateau, dividing the 

 mesa into what appear isolated masses, but which are all con- 

 nected. One isthmus, from 3 to 12 feet in width and 125 in length, 

 connected a plateau of several miles extent with the main mesa. 

 The highest portion of this mass is on the east side ; and from the 

 base of the almost continuous cliffs which border it the country 

 descends in long, timbered slopes to the broad open area of Egeria 

 Park, lying between them and the Park range." 



It was examined. Dr. Hayden states, " in the usual manner of 

 the surve)'" — a carefully coloured geological map, showing the 

 distribution and extent of the rocks, together with numerous sections 

 and memoranda relative to the abundance and occurrence of the 

 economical deposits, being prepared ; and then this is adapted to a 

 careful trigonometrical survey of 4 miles to the inch, with 2U0-feet 

 contours. This latter is reduced one half for publication. 



Speaking generally, " the older metamorjjhic rocks, such as the 

 granites, schists, &c., of probably Archaean age, in which alone the 

 precious metals and minerals of Colorado have been found, ajid which 

 form the foundations on which aU the bedded rocks, sandstones, 

 limestones, &c. of the country rest, are brought to the surface and 

 exposed only along the folded ridges of the Park range, and in the 

 bottoms of a few caiions in some of the southern tributaries of the 

 White Eiver and of the neighbouring tributaries of the Grand." 

 Along the northern portions of the district, and in the extreme west, 

 the surface of the country is mainly composed of Cretaceous rocks, 

 either horizontal or only slightly undulating. The coal, a fairly 

 good lignite, lies in the upper, middle, and lower portions of this 

 group, in definite horizons ; but it improves in quantity and quality 

 to the westward. It is in the south-eastern portion, however, near 

 the Grand and Eagle rivers, that the sedimentary rocks, among 

 which occur quantities of limestone and exter.sive deposits of gyp- 



