398 



NATURE 



{Sept. 12, 1872 



Nine-tenths of the area is covered with volcanic material 

 in some form. The base rocks are the usual metamor- 

 phic g:ranitoid scries of the country, with basilts and 

 basiltic ccini;lomerates in every variety. Tlie sedimentary 

 rocks belong to the Carboniferous, Jurassic, Cretaceous, 

 and Tertiary ages. The Triassic is probably wanting. 

 The sedimentary rocks occur in patches, covering very 

 restricted areas, yet presenting evidence that, up to the 

 period of the Eocene Tertiary inclusive, they were extended 

 uninterruptedly over the whole country. In the Yellowston; 



valley, as in the valleys of all the streams of the West, 

 there is a chain of lake basins that must have existed 

 di'.iing the Pliocene period. There was a continuous 

 cli.iM of these lakes of greater or less size to the source of 

 the river ; thence it expanded into an immense double 

 lake, of which only a remnant, Yellowstone Lake, now 

 remains. This lake was once much larger than at pre- 

 sent, and it was partially connected with another lake 

 about 30 miles long and 20 wide, which terminated at the 

 Grand Caiion, at the upper falls of the Yellowstone. ;_ 



'A«ii' 



y^m%'/0 r: ix""- ..-4 



■'i'mdir.ijf^' 



:;^^Mr 



ii&-<^mmuii. 





ms 





K'-OiiSiMudVule. 





ISuZphurSppi 





^t% 





■'•''?€%» 

 '<'/!',^^ 



Xeet 



Jj6aa- 



-Sulphiir and Mud SpriiiKs EIjI-' Mile? below Ytllov.stnne I.al;e 



The term 'S'cllowstone liasin is sometimes applied to 

 the entire valley ; but the basin proper comprises only 

 that portion enclosed within the remarkable ranges of 

 mountains which give origin to the waters of the Yellow- 

 stone, south of Mount Washburne and the Grand Canon. 

 This basin is about 40 miles in length from north to 

 south, and on an average 30 miles in width from east 

 to west. It might be called the vast crater of an ancient 

 volcano made up of thousands of smaller rents and fissures, 

 out of which the lluid interior of the earth, fragments of 



rocks, and volcanic dust have been erupted in unlimited 

 quantities. Hundreds of the nuclei or cones of these vol- 

 canic rents are now remaining, some of them rising to a 

 hci_;ht of nearly i i,ooo feet absve the sea. Indeed, as 

 has been said, the hot springs and geysers of this region 

 ate only the closing stages of that wonderful period of 

 vol:anic action which began in Tertiary times. Even at 

 the present time there are connected with these manifesta- 

 tions of internal heat earthquake phenomena which are 

 wcii worthy of attention, iuinhquake shocks are not 



