GEOLOGY. 293 



sand, which is found at the bottom of the streams, generally at the 

 upper end of sand-bars. The sand having been separated from the 

 coarse gravel, on examining it closely with the microscope, there ap- 

 pear interspersed through it red particles of different shades, and 

 some few yellow and green particles ; of the former, some appear to 

 be colored quartz, while others are garnets and probably pyrope. The 

 black particles are readily separated into two sorts by the magnet ; 

 one of these is evidently magnetic oxide of iron, while the other 

 agrees precisely with Dr. Thompson's description of titanate of iron, 

 or menaccanite. The gold is in flat scales. This new gold field is not 

 likely to prove profitable for working, but is interesting in a geological 

 and mineralogical point of view. Journal of Franklin Institute, June. 



Quartz rock, containing disseminated particles of gold, has been 

 noticed during the past summer, as having been obtained from various 

 localities in the Lake Superior mining region. This, however, is not 

 the first discovery of gold on the lake ; geologists have detected it in 

 several instances, and the late Dr. Houghton was confident that gold 

 would be found in considerable quantities ; and it has been supposed, 

 from minutes made by him and from remarks on the subject, that he 

 knew more about its location than any one else, and even much more 

 than he had ever made known. 



In New Grenada. M. Boucard, in a paper presented to the French 

 Academy upon the geology of the provinces of Panama and Yeraguas, 

 in New Grenada, observes that the igneous rocks, whose upheaval has 

 formed the Cordilleras, are frequently penetrated by veins of aurifer- 

 ous quartz, running north and south. The hard rock which composes 

 these veins has resisted atmospheric influences better than the sur- 

 rounding rock, and the veins consequently project so as to be easily 

 seen. The proportion of gold very rarely amounts to one 2,000th, 

 which is of course too small to pay for working. 



GEOLOGY OF THE CALIFORNIA GOLD REGIONS. 



NEAR the summit of the Sierra, granite is the prevailing rock. On 

 the flanks of the mountains and in the valleys, metamorphic and igne- 

 ous rocks occur, with occasional veins of trap, having a close, com- 

 pact structure. There was by no means so great a variety of meta- 

 morphic rocks observed on the western flanks of the Sierra as might 

 have been expected. North of the American River, no others were seen 

 but varieties of talcose slates and argillites. Between the Cosumes and 

 the Calavares Rivers there were, in addition, hornblende and hard sili- 

 cious talcose slates. This latter region also furnished testimeny to a 

 greater intensity of the action of heat in the greater abundance of in- 

 durated slates. The extensive region throughout which these slates 

 abound shows that they once occupied a large area, which has been 

 materially lessened by the intrusion of masses of igneous rocks in innu- 

 merable places. The intrusive rocks in this region are chiefly trap, 

 sienite, porphyry, and serpentine. The region between Feather River 

 and the American River bears evidence of having become quiescent, or 

 nearly so, long before the comparatively recent period, when the country 



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