The Geoloa-ical Structure 



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4. Very coarse syenitic conglomerate, forming a second ridge. 

 Some masses of stone two feet in diameter, were observed in this 

 bed. It occupies a breadth of 160 yards. 



The thickness represented by these measurements maybe about 

 2,000 feet ; but this by no means includes the whole thickness 

 of similar rocks developed at Maimanse, and which extend both 

 above and below the beds above described. The total thickness 

 seen at Maimanse, is estimated by Sir W. E. Logan at 10,000 

 feet. 



The beds included in No. 3 of the above section, are those in 

 which the principal indications of copper have been observed. 

 On the summit of the ridge, the hard semi-crystalline trap is tra- 

 versed by a narrow fissure, running nearly with the strike of the 

 beds, or north and south. Its greatest thickness is about 6 

 inches, but in some places this has been found to be nearly filled 

 with native copper. One mass weighing 600 lbs. has been ex- 

 tracted, and the whole yield of a shaft 27 feet deep and without 

 galleries, has been about three tons. The veinstones here are 

 principally calc spar and quartz. 



At a short distance westward of the shaft, the vein is divided 

 into two branches. The course of this vein, as well^as of most others 

 in these hills, is marked by surface trenches, usually called " In- 

 dian diggings," though they are evidently erosions similar to those 

 which run along the veins seen on the present beach, and exca- 

 vated when the surface was undergoing denudation under water. 

 These trenches, however, afford excellent guides in tracing the 

 veins, and they have served this purpose to the ancient Indian 

 miners, in whose time it is likely that plates of metallic copper, 

 exposed by the removal of less resisting materials, may in places 

 have projected from the bottom of these furrows. The real Indian 

 diggings are shallow holes, sunk at intervals along the courses of 

 the veins, and surroimded by broken pieces of veinstone, along 

 with which are occasionally found stone hammers. These ham- 

 mers are merely beach pebbles, usually of trap, and having shal- 

 low grooves worked around them, to receive withes or thongs used 

 as handles. Most of them are 5 or 6 inches in their longest 

 diameter, but one, now in the collection of the Geological Survey, 

 is about a foot in length. 



About one hundred yards northward of the shaft just men- 

 tioned, excavations have been made at the intersection of two 

 veins, one running NW. and SE., the other l!^. and S, The 



