GEOLOGY — HOT SPRINGS — METAMORPHOSED TUFAS. 49 



caiion exhibiting the typical form of trap stairs. Crossing to Chit-tike creek, the same formation 

 reappears, apparently undisturbed ; the canons of several confluent streams flowing from Mount 

 Jefferson having here cut the plateau into a series of narrow ridges, perhaps a thousand feet in 

 height, crowned witli a layer of trap, which closely resembles a wall of artificial masonry, built 

 on an immense artificial embankment. 



The east wall of the caiion of the Des Chutes river at this point consists of a layer of trap a 

 hundred feet in thickness, composed of perpendicular columns, from the base of which it slopes 

 away to the water's edge. The course of the stream, marked with geometrical precision by the 

 lines and angles of the stratum of trap stretching off for many miles in perspective, vividly re- 

 called the cyclopean architecture which gives so impressive a character to Martin's paintings. 



On going over to the valley of Warn Chuck river, still another tributary of the Des Chutes 

 from the Cascades, we found a marked change had taken place in the stratified tufas, which are 

 so characteristic of the geology of all this region. 



Hot Springs. — At different points along the valley of Warn Chuck river, hot springs issue 

 from the base of the cliffs which bound it. The number of these springs is large, and two or 

 three of them are quite copious. They issue from fissures in the rock, the water flowing from 

 them collecting in basins of several feet in diameter, thence flowing into the Warn Chuck river, 

 and giving it its name. The temperature of two of these springs was respectively 143° and 

 145°. The water holds large quantities of silica in solution, but has a bland and pleasant 

 taste, and, when cooled and drank, has, apparently, no medicinal effect. The quantity of silica 

 is, however, very large ; the basins in which the water collects containing floating masses of 

 gelatinous silica, of which the surfaces are tinged with a green color, which I have supposed 

 was derived from silicate of iron. The sides of these basins, and of the streams flowing from 

 them, are encrusted with a white frothy silicious deposit, which also invests whatever stones, 

 sticks, or other foreign substances project from the surface of the water. 



Metamorphosed Tufas. — The cliffs which border Warn Chuck river, in the vicinity of the 

 warm springs, are apparently composed of the same or a similar series of volcanic tufas and 

 marls with those described as forming the banks of Mpto-ly-as river, Psuc-see-que and Chit-tike 

 creeks, but here so changed as hardly to be recognized at first sight. They are traversed by a 

 thousand cracks and fissures, from which the steam or water of the hot springs emanate, by 

 which the aspect of the rock has been made to resemble that of serpentine or some light colored 

 volcanic or metamorphic rock which has suffered complete fusion. Upon closer examination, 

 however, many of the varieties of tufaceous rock exposed in the localities referred to above may 

 be here recognized, but presenting such changes of physical character and composition as would 

 deceive the most practised observer, until he had obtained a series which exhibited all the 

 successive grades of metamorphosis. The white, chalk-like, infusorial marls are, by the action 

 of these hot silicious springs, first rendered harder and more dense without marked change of 

 color, subsequently becoming still more consolidated ; the extreme form of metamorphism of 

 this variety being a jasper, colored red or green by the silicate or oxide of iron, closely resem- 

 bling the porcelain jaspers of Germany. 



The coarser tufas, such as that described as occuring on Psuc-see-que creek, composed of lumps 

 of fine felspathic pumice, resembling kaolin, cemented by a fine sediment, exhibit more dis- 

 tinct and interesting grades of change. The cement is first consolidated — sometimes remaining 

 bluish-white, sometimes tinged with green — the balls of cotton-like pumice being scarcely 

 changed ; second, the cement has become hard and almost crystaline, somewhat resembling 

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