412 



SCIENCE. 



[N. S. Vol. XV. No. 376. 



saurus. The tibia and fibula are longer 

 than in that genus and are separated by a 

 wide cleft. The anterior arch is ichthyo- 

 saurian excepting the scapula which is 

 very broad. The posterior arch is very dif- 

 ferent from that of Ichthyosaurus. The 

 skull is not well known. The dentition re- 

 sembles that of Mixosaurus. The forms of 

 this genus represent a distinct group of 

 the Ichthyosaiiria. In some respects they 

 are generalized and resemble Mixosaunis, 

 in the other characters they show special- 

 izations which separate them from the 

 other members of the family. 



Ore Deposits of Shasta County: F. M. 



Anderson, Berkeley, Cal. 



The copper belt of Shasta County, Cali- 

 fornia, embraces, geologically, a series of 

 ■old sedimentary rocks, -Devonian, Car- 

 honiferous and Triassic, Avhicli extend in 

 somewhat parallel bands northeasterly and 

 ■southeasterly across the course of its longer 

 axis. These strata have been penetrated 

 and disturbed by intrusions of acid grano- 

 lite, generally of the character of granite 

 porphyry, though variable, which have 

 been accompanied by flows of rhyolite and 

 lavas resembling trachyte. In the vicinity 

 of these intrusions and generally enclosed 

 in the metamorphosed sedimentary rocks oc- 

 cur the deposits of sulphide ore which forms 

 the subject of this paper. There are three 

 or more types of ore represented among 

 these deposits. The first class includes de- 

 posits found to the south of Pitt river near 

 the mouth of the McCloud. They consist 

 essentially of lenticular bodies of pyrrhotite 

 carrying pyrite and chalcopyrite, but on 

 the whole a Ioav percentage of copper. 

 These pyrrhotite bodies sometimes reach a 

 thickness of 8 or 10 feet and a length of 

 50 or 60 feet, and are apparently connected 

 vrith intrusions of dioritic rock. The second 

 class of deposits is represented in all of the 

 large ore bodies west of the Sacramento 



river, including the proiDcrties of the 

 Shasta King, Balaklala, Iron Mountain and 

 Mammoth mines. They are immense bodies 

 of sulpiride ore, consisting almost entirely 

 of pyrite and chalcopyrite, with compara- 

 tively little zinc blende, but carrying both 

 silver and gold. They appear to be re- 

 placement deposits, and have preserved in 

 a measure the banded or stratified form of 

 the original rocks. The largest of these de- 

 posits approximates 2,000,000 tons in ex- 

 tent. The grade of the ore varies from 1 

 to 20 per cent, in copper, averaging gener- 

 ally between 3 and 7 per cent., and carry- 

 ing silver and gold to the value of $2.50 

 per ton. The ores of the Pittsburg and 

 Afterthought districts, which constitute the 

 third class, are similar to each other in 

 character and probably in the mode of their 

 occurrence. They are comparatively poor 

 in iron and contain a larger percentage of 

 zinc blende than any of the others. The 

 ore includes little pyrite, consisting largely 

 of chalcocite, bornite, chalcopyrite and 

 other rich sulphides, with a gangue of silica 

 and barite. The average grade of the ore 

 at Bully Hill is nearly 10 per cent, copper 

 with a relatively high value in silver and 

 gold. The surface alteration in these de- 

 posits has resulted in the removal of the 

 copper contents from the upper levels in 

 which there is considerable concentration of 

 gold and silver. In many cases the copper 

 has found secondary lodgment in lower por- 

 tions of the deposit, forming what is some- 

 times designated the ' copper level. ' This 

 secondary enrichment of the ore bodies is 

 the rule throughout the whole extent of the 

 copper belt. The grade and magnitude of 

 these sulphide deposits entitle them to rank 

 among the most important in the United 

 States. 



Lake Chelan, Washington: H. W. Fair- 

 banks, Berkeley, Cal. 

 Lake Chelan is one of the most remark- 



