Reviews — The United States Geological Survey. 471 



the fjords of this area are due, not to glacial erosion, but to the 

 drowning of a drainage system only slightly modified by glaciation. 



The whole of the area between the Coast Range and the coast is 

 occupied by a group of slates and greywackes known as the Eerners 

 Formation, probably of late Mesozoic age. These are intercalated 

 with volcanic breccias, tuffs, and augite melaphyres. The Coast 

 Range itself consists of quartz-diorite, which is regarded as of late 

 Cretaceous age. The slates become metamorphosed into schists in 

 the neighbourhood of the quartz-diorite, which itself is markedly 

 gneissose at its margins. 



The gold belt is contained wholly within the slates ; there are no 

 prospects in the schists or in the quartz-diorite. Ore-bodies occur 

 either as stringers, fissure veins, or occasionally as mineralized 

 dykes. 



The dykes belong to a group of minor intrusions of uncertain age, 

 and include diorites, albite diorites, lamprophyres, and gabbros. Their 

 mineralization usually takes the form of intense albitization. 

 Another frequent result is the production of abundant apatite in the 

 altered wall-rocks. Some of these mineralized dykes carry low- 

 grade gold ores, which indicates a magmatic origin for the gold 

 deposits in this area. 



Pillow-lavas are recorded at one locality, and their occurrence 

 in an area in which albitization is so prominent a feature would 

 suggest affinities with the spilitic facies. However, the pillow-lavas 

 appear to consist of augite with only a little interstitial material of low 

 refractive index and to belong to the augite melaphyre series of the 

 Eerners Formation, whereas the albitization takes place in dykes 

 probably younger than the quartz-diorite of the Coast E.ange. 



The bulletin contains details of the gold prospects in the area, and 

 the geological work has done much to show in what directions fresh 

 ore-bodies should be sought. 



2. ExjLLETm 503. Iron-ore Deposits of the Eagle Mountains, 

 Califoenia. By E. C. Harder, pp. 81, with 4 figures in the 

 text and 13 plates (including 6 maps). 1912. 



SITUATED in the waterless desert of South Califoi'nia, and some 

 40 miles from the nearest railway, the Eagle Mountains had 

 been visited only by hasty prospecting parties until the district was 

 surveyed in 1909. This survey located deposits of very pure iron-ore, 

 and it is estimated that about fifty million tons of good ore are 

 available in the northern part of the range. It is thought that the 

 establishment of blast furnaces and steel plants in South California 

 will have for its immediate result the development of these Eagle 

 Mountain ores. 



The geological structure of the northern part of the range is that 

 of an oval dome. The centre is occupied by a small outcrop of gneiss 

 and schist ; these are surrounded by a series of quartzites and schistose 

 arkose, overlain by a second quartzite with interbedded dolomite 

 lenticles. Into these beds two large sills of quartz-monzonite have 

 been intruded, causing the metamorphism of the quartzites and 

 dolomite. It is in the dolomite horizons and in the surrounding 



