128 QUICKSILTER DErOSITS OF THE PACIFIC SLOFE. 



Serpentine is also converted into carbonates of lime and magnesia in 

 the Coast Ranges, and the process can be followed in detail in some cases. 

 No. 223, Knoxville, is a grayish-green serpentine full of minute veins, the 

 material of which does not effervesce with cold, dilute chlorhydric acid. 

 Under the microscope these veins are seen to be composed of carbonates 

 often exhibiting cleavage. On removing the cover it was found that a 

 portion of the carbonates dissolved slowly in cold acid, while a portion 

 remained unattached. Dolomite and magnesite are thus probably both 

 present. No attempt was made to determine the quantity of magnesia 

 in these carbonates. 



It is manifest from this slide that the substance of the serpentine has 

 actually been replaced, for the masses between the veins are rounded and 

 would no longer fit together were the veins removed. The result is a net- 

 structure similar to that observed when olivine is decomposed to serpentine. 



METAMORPHIC ROCKS OF UNCERTAIN AGE. 



Gaviian Range and Steamboat rocks. — In the forcgoiug pages tliosc metamorphic 

 rocks only have been considered which are actually known to be of Knox- 

 ville age or which there are good grounds for referring to that epoch. In 

 the course of this investigation metamorphic rocks of uncertain age have 

 been encountered at two localities. One of these is in the Gaviian Range, 

 where an extraordinarily crystalline limestone is associated with granite 

 and gneissoid rocks. The occurrence is so different from the remainder of 

 the altered rocks of tiie Coast Ranges examined that it could not be referred 

 to the same series without much more investigation than it has been prac- 

 ticable to devote to it. I suspect it to be of far greater age than the rest 

 of the exposures. Under the microscope the gneissoid rock is found to be 

 of the Archaean gneiss tj'pe. It is chiefly composed of quartz, orthoclase, 

 plagioclase, and biotite. There is a decided tendency to granophyric 

 structure, and veins and clusters of fibrolite are abundant. This rock con- 

 tains no zoisite. 



At Steamboat Springs the sedimentary rocks are greatly disturbed and 

 in part highly metamorphosed. They seem to belong to the series re- 

 garded as Jura-Trias by the geologists of tlie fortieth parallel, and are 

 certainl\- older than the Tertiary. The area examined is too small to 



