1854.] 



WILSON — CALIFORNIA GOLD-FIELDS. 



317 



nearly its original height. A high cliff, on the eastern side, exposes 

 to view seven distinct strata, the upper one of which is composed of 

 volcanic cinders cemented with lime (fig. .5) ; the others are pi'incipally 

 conglomerates, composed of granite boulders and calcareous deposits. 

 Some of the boulders are extremely large and smoothly rounded ; 

 one which I measured was 8 feet in its greatest diameter. 



Fig. 5. — Section at Murphif s Deep Big gings. Length about |^mile. 



N.N.W. 



Gold-diggers' shafts, 90 feet deep. 



Mica slate 



1 . Volcanic ashes. 



2. Sandy limestone. 



3. Sandy limestone with boulders. 



4. Limestone with sand and boul- 



ders ; the beds being more cal- 

 careous downwards. 



Blica slate. 



5. Shafts, go feet deep, piercing cal- 

 careous deposits, with boulders in 

 the lower part, and reaching the 

 auriferous clay that rests on the 

 mica-slate. 



Mode of formation of the Auriferous Drift. — To account for 

 the manner in which the various rocks are arranged in the boulder 

 conglomerate, I would suppose that the quartz-boulders of the lower 

 strata belong to the veins of that rock in the neighbouring hills, 

 which, after being left bare by the wasting of the slate-rock, and rent 

 by frost or otherwise, rolled down into the creeks and rivers, and as 

 the sea gradually encroached, these creeks and rivers would become 

 bays and inlets, round the margins of which ice-banks might be 

 formed, which at times of thaw and heavy floods would be detached 

 and carried out to sea, with such attached matter as it could float ; 

 where meeting with north-west winds and the southward current of 

 the ocean, they were drifted south and east, until they got stranded 

 on or against the hills which then formed the sea-shore. But as the 

 land continued to be submerged, the water penetrated farther among 

 the hills and at length reached the granite ranges, from whence it 

 carried out the granite drift while the quartz was protected by depth 

 of water. 



There are several of these tertiary? hills under which gold is 

 found ; but no gold is found in them, except at their immediate con- 

 tact with the older rocks ; which may be accounted for in this way. 

 First, that when quartz is auriferous, it is highly impregnated with 

 iron also, which on exposure to the atmosphere oxidizes and causes 

 a disintegration of the rock, by which means the gold is liberated ; 

 which, if it then be drifted by water, settles in the lower stratum, 

 and is in consequence less likely to be removed by either ice or water. 



