December 13, 1895.] 



SCIENCE. 



791 



northern California, between the Sacra- 

 mento Valley and the Great Basin, and ad- 

 joins the northern end of the Sierra Nevada. 

 It is bounded by the 121st and 122d merid- 

 ians and the 40th and 41st parallels, and 

 contains an area of 3,6.34.4 squ.are miles. 



Within the district there are three dis- 

 tinct topographic features. Beginning at 

 the west, it includes (1) a small portion of 

 the eastern border of the Sacramento Val- 

 ley, (2) the Lassen Peak volcanic ridge, 

 and (3), upon the east, a portion of the 

 Great Basin platform. 



Twenty-two geological formations are 

 shown upon the map. Thirteen of these 

 were deposited by water as sedimentary 

 rocks. The remaining nine are of igneous 

 origin, and were erupted from the interior 

 of the earth in a molten condition. Some 

 of the sedimentary rocks, especiallj^ the 

 younger ones, have not been materially 

 changed since they were deposited, but 

 others, such as the Auriferous slates, have 

 been greatly altered or metamorphosed, 

 and contain veins of quartz and metallif- 

 erous deposits. 



By far the most abundant rocks of the 

 Lassen Peak district are those of igneous 

 origin. The numerous volcanoes of the 

 district have furnished a great variety of 

 such rocks. 



Beds of unaltered stratified rocks, none 

 of which are older than the Cretaceous, are 

 still nearly horizontal; although uplifted, 

 they have not been compressed enough to 

 produce folds. On the other hand, the 

 Auriferous slates have been thrown into a 

 series of anticlines and synclines and so 

 greatly compressed as not only to close the 

 folds, leaving the strata in many cases ap- 

 proximately vertical, but also to break and 

 displace them along a series of thrust faults 

 during the earth movements by which the 

 mountains were produced. 



Upon the economic map special attention 

 is called to the distribution of auriferous 



slates, in which alone there is any prob- 

 abilitj^ of discovering valuable deposits of 

 precious metals. These rocks are exposed 

 in the southeastern and northwestern por- 

 tions of the area mapped, and extend through 

 under the lavas of the Lassen Peak district 

 from the Sierra Nevada to the Klamath 

 Mountains of the Coast Kange. The broad 

 stretch of unaltered lavas about Lassen 

 Peak does not contain any appreciable 

 amount of precious metals, and may be 

 wholly neglected by the prospector. 



Among the auriferous slates seven for- 

 mations have been distinguished, ranging 

 in age from the Silurian to the Jurassic, in- 

 clusive. Of these the Cedar formation, of 

 Triassic age, has been the most productive. 

 By its disintegration it has furnished the 

 gold for the placer mines of Indian Creek 

 below Shoo Fly, of Soda Creek, Kush Creek, 

 the north fork of Feather Eiver and Dutch 

 Hill. The Savercool mine, by the north 

 fork of Feather Eiver, is on this belt, and 

 active prospecting is going on at a number 

 of points. Numerous copper deposits have 

 been discovered in the Pit Eiver region. 



Intermingled with the auriferous slates, 

 there are eruptive rocks, such as diabase, 

 porphyrite, peridotite and diorite, which 

 have much to do in determining the distri- 

 bution of certain classes of ore bodies. The 

 areas of eruptive rocks have been outlined, 

 and it has been found that the most promis- 

 ing prospects of that region are located near 

 the borders of these eruptive masses. The 

 ore deposits may be in the auriferous slates 

 or the eruptive rock, but in either case they 

 are not far from the contact. 



Traces of coal have been discovered in 

 the Chico and lone formations, but no de- 

 posits of considerable value are yet known 

 in the region of Lassen Peak. The Tuscan 

 tuff has furnished some excellent material 

 for chimneys, hearths and water coolers. 

 The large deposit of diatom earth on Pit 

 Eiver, having a thickness of over 100 feet 



