GEOLOGY. 289 



tioned experiments. To account,, therefore, for the origin of carbonic 

 acid exhalations, we need no more assume that the focus must be where 

 red heat exists, which presupposes a depth of at least five miles (Ger- 

 man) ; for the clay slate or any other sedimentary formation may be 

 the seat of the evolution of the gas, since only in the moderate depths 

 of about half a mile (German) the materials required are present. 



OX THE GEYSERS OF CALIFORNIA. 



PROF. FOREST SHEPHERD, in a communication published in Silliman's 

 Journal, September, 1851, gives an account of some remarkable geysers 

 by him discovered north-west of the Napa Valley, California. Mr. 

 Shepherd, having noticed what he conceived to be a line of thermal 

 action in the Napa Valley, especially near the foot of Mount St. Helena, 

 determined to trace it, and find its seat or focus of greatest intensity. 

 With this object in view, he travelled, in company with a select party, 

 in a direction north-west of the Xapa Valley, and, after encamping one 

 or two nights in the rain, and wandering through almost impenetrable 

 thickets, reached the summit of a high peak on the morning of the 

 fourth day. The scene presented from this point is described as fol- 

 lows : " On the north, almost immediately at our feet, there opened 

 an immense chasm, apparently formed by the rending of the mountains 

 in a direction from west to east. The sun's rays had already pene- 

 trated into the narrow valley, and so lighted up the deep defile, that, 

 from a distance of four or five miles, we distinctly saw clouds and dense 



i/ 



columns of steam rapidly rising from the banks of the little river Pluton. 

 It was now the 8th of February ; the mountain peaks in the distance 

 were covered with snow, while the valley at our feet wore the verdant 

 garb of summer. It was with difficulty we could persuade ourseltes 

 that we were not looking down upon some manufacturing city, until, 

 by a tortuous descent, we arrived at the spot where at once the secrets 

 of the inner world opened upon our astonished senses. In the 

 space of a half a mile square we discovered from one to two hundred 

 openings, through which the steam issued with violence, sending up 

 columns of dense vapor to the height of one hundred and fifty to two 

 hundred feet. The roar of the largest tubes could be heard for a mile 

 or more, and the sharp hissing of the smaller ones is still ringing in my 

 ears. Many of them would work spasmodically, precisely like high 

 pressure engines, throwing out occasional jets of steam, or volumes of 

 hot, scalding water, some twenty or thirty feet, endangering the lives 

 of those who rashly ventured too near. In some places the steam and 

 water come in contact so as to produce a constant 'jet d'eau^ or 

 spouting fountain, with a dense cloud above the spray, affording vivid 

 prismatic hues in the sunshine. Numerous cones are formed by the 

 accumulation of various mineral salts, and a deposit of sulphur crystals 

 with earthy matter, which often harden into crusts of greater or less 

 strength and thickness. Frequently the streams of boiling water would 

 mount up to the top of the cones with violent ebullition. Some of the 

 cones appear to be immense boiling caldrons, and you hear the lash- 

 ing and foaming gyrations beneath your feet as you approach them. 



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