a King—Geology of the 4.0ih Parallel 



The geological exploration of the fortieth parallel has cov- 

 ered an east and west section of the Cordilleras from the 104th 

 to the 120th meridian, or from the east base of the Kocky 

 Mountains to the eastern boundary of California, along the 

 fortieth and forty-first parallels. The belt of territory under 

 examination is a little over one hundred miles from north to 

 soutn. Over the greater part of this area bodies of Paleozoic 

 rocks are observed at intervals. A considerable study of these 

 more or less detached exposures, together with the final deter- 

 mination of a large collection of molluscan fossils, has rendered 

 it possible for us to correlate the various members of the series, 

 and construct with considerable precision a complete Paleozoic 

 section. It is the object of this paper to announce the strati- 

 graphical divisions established in the field, and their relation 

 to the Paleozoic subdivisions as established in New York and 

 in the Mississippi basin. 



It may be well to remark that along our eastern boundary, 

 in the region of the Eocky Mountains, the entire Paleozoic 

 series — including Coal-measure beds and strata bearing Potsdam 

 fossils — are embraced within a section from 900 to 1200 feet, 

 the whole entirely conformable and resting discordantly upon 

 an Archaean foundation. In passing westward the series rap- 

 idly expands from 1,000 to 32,000 feet Lithologically, divis- 

 ions which were lost in the narrow Rocky Mountain Paleozoic 

 zone are established with great volume and persistency over 

 wide areas in Utah and middle Nevada. Finally, in the neigh- 

 borhood of Battle Mountain, at longitude about 117'' 25', an 

 Archaean land-mass rose to the west of the Paleozoic ocean, 

 interrupting farther continuance in that direction. 



Tiie region of the Rocky Mountains represented Archsean 

 islands and shallows, around and over which the sparing sedi- 

 ments were deposited, while toward the westward the general 

 contour of the Paleozoic ocean deepened over a broad basin, 

 which probably continued to a great depth quite against the 

 western shore in longitude 117° 30'. To the southward, from 

 the well-known observations of Dr. Newberry and others, it is 

 evident that this Paleozoic sea very perceptibly shallowed. 

 The northern configuration of the bottom and the depth of the 

 Paleozoic series in at present unknown. It is a striking fact, 

 that wherever, within the limits of this exploration, exposures 

 are made, — and they are very frequent, — from the Primordial 

 to the summit of the Coal-measures, there is never the slightest 

 unconformity between the various members of the series. The 



