134 Prof. J. B. Dana on some Results of 



none yet known; and if none really occurred, then the con- 

 tracting globe at that time, as far as U. S. North America is 

 concerned, must have expended its energies (which it had been 

 gathering during the Palaeozoic) in making the Alleghanies, and 

 in some minor plications along the Acadian region. 



The " Great Basin/'' between the Sierra Nevada on its western 

 border and the Wahsatch range on its eastern (lying along the 

 meridian just east of the Great Salt Lake), contains a number 

 of short ridges parallel to these lofty border ranges, some of 

 which are quite high* ; and they consist, according to King, " of 

 folds of the infra-Jurassic rocks ;" and "it is common to find no 

 rocks higher than the Carboniferous/' owing, it is stated, to the 

 erosion that has taken place. It is not clear that part, at least, 

 of the Great Basin plications may not have taken place before 

 the Jurassic era. If not^ then the movements must have been 

 in some way involved with those of the Sierra and Wahsatch 

 regions f. 



4. At the close of the Jurassic two great geosynclinals, which 

 had been in progress through the Palaeozoic and until this 

 epoch in the Mesozoic, culminated each in the making of a 

 lofty synclinorium :— -one the Sierra Nevada, some of whose 

 summits are over 14,000 feet high ; the other the high Wah- 

 satch, a parallel north and south range. 



Whitney has proved that the Carboniferous and Jurassic 

 rocks are comformable in the Sierra-Nevada range, and that 

 the close of the Jurassic was the epoch of its origin ; but direct 

 proof is not yet found that the Devonian and Silurian forma- 



* An admirable chart, giving in detail the topography of this whole 

 region and including the Wahsatch, has been prepared by Mr. James T. 

 Gardner, after careful surveys by himself, topographical surveyor of the 

 Exploration of the Fortieth Parallel under Clarence King, and is now 

 ready for the engraver. Mr. King has published thus far only brief chap- 

 ters on the geological results of his survey in the volume of J. T. Hague 

 on Mining Industry, vol. iii. He has ready for publication vols. i. and 

 ii., on Systematic and Descriptive Geology. The Botanical Report of the 

 Survey, vol. v., has been issued ; but vol. iv., on Zoology and Palaeonto- 

 logy, remains to be completed. 



t Mr. James T. Gardner, in a letter of May 8th, informs me that in his 

 opinion all the more important mountain-ranges of the Great Basin (in 

 Nevada) are included in a chain trending about N. 40° E., the whole having 

 a breadth across the trend of 120 miles. Austin, in Nevada, lies near the 

 centre line of the chain. To the west of this elevated region is the great 

 depression where the rivers of Nevada evaporate in Carson, Humboldt, 

 Pyramid, Mud, and other lakes ; and to the east is the great depressed area 

 of Salt Lake. On this view, if these mountains were made at the close of 

 the Jurassic, there were formed at this epoch three lofty synclinoria (the 

 Sierra, the Humboldt, and the Wahsatch) on the western-border, central, 

 and eastern- border chains of the Great Basin. The precise determination 

 of the epoch of origin of the Humboldt chain is therefore of much im- 

 portance. 



