I>ERIVATION OF SERPENTINE. 117 



tropic, and when separated gives a strong chromium reaction. Numerous 

 deposits of chromic iron intimately associated with serpentine ni-e known 

 in the Coast Ranges. Magnetite is ahnost always present. 



The origin of serper,tine._No extended histoHcal acconnt of the views held 

 of the origin of serpentine is necessary here. The present investigation is 

 not founded on any similar inquiry, nor do I suppose that all serpentines 

 in other regions have had an origin similar to that of the serpentine of the 

 Coast Ranges. A few historicnl notes, however, may serve to refresh the 

 reader's memory. 



The occurrence of serpentine in dikes led to its classification as an 

 eruptive rock by the earlier geologists, who were unaware of its composi- 

 tion, and even long after it was known to be a liydrated mineral there are 

 frequent references to it in the literature, unaccompanied by any qualifi- 

 cation or explanation, in which it is classified as igneons. The close and 

 frequent connection between gabbro and serpentine led L. von Buch, in 

 1810, to suppose that serpentine was a dense or cryptocrystalline form of 

 that rock. This suggestion is interesting as showing how long the relation- 

 ship of the rocks has been recognized. Direct eruption of the serpentines 

 has also been maintained, in a modified form, by more recent Italian geolo- 

 gists, who suppose outbursts from the depths of the earth of a hydrated, 

 magnesian mud which consolidated to serpentine. 



° In 1857 Dr. T. Sterry Hunt showed that when a mixture of magnesium 

 carbonate and free silica is heated in a solution of alkaline carbonate a 

 hydrous, magnesian silicate is formed and the alkaline carbonate is re- 

 generated. He soon afterwards came to the conclusion that this process, 

 though locally important, would not explain the greater part of the occur- 

 rences. In 1860 he proposed as an explanation of the massive serpentines 

 the reaction between the soluble silicates of lime and alkalis from decaying 

 rocks and the magnesian salts of natural waters. Dr. Hunt admits, however, 

 that serpentines are also formed by epigenesis, at least from olivine and 

 enstatite.^ Dr. Hunt's view, while not generally accepted, has earnest 

 advocates, and some geologists who reject this theory for a majority of 

 eases believe it to be the true explanat ion of some occurrences. ^ 



■ roeol. History of Serpentines, 1883, v> IH ; Origin of Crystalline Eocks, 1H^4, s^ 105. 



