250 



Memoir on the Geology of the 



[Oct. 



Gradation Hall, between the road and the margin of the lake, in its N. 

 E. extremity, has a compact, metallic structure, highly magnetic, with 

 hardly any quartz (No. 17) : a few yards to the southwest, the vein con- 

 tains a good deal of quartz ; the metal is more oxidated, although main- 

 taining still its magnetic powers (No. 18). Following the vein in the 

 same direction, we see it appear in the opposite side of the lake, in the 

 hanks of the road, which goes round and close to the lake. There the ore 

 has lost a good deal of its quartz ; the iron is more oxidated, and the rock 

 assumes a kind of columnar structure (No. 19). This is the appearance of 

 the vein in the section for the road. But the out-croppings of the vein at 

 top of the same hillock are compact, scabrous, and of a slight cellular 

 texture (No. 20). Going on always S. W., we sec the same vein conti- 

 nued over the next hill, close to the road going to the Koondah ; and so 

 much divested of iron, that it resembles a friable stratified sandstone, 

 the quartz being granular (No. 21). 



It is in this kind of magnetic iron ore, particularly in the blocks 

 below Gradation Hall, that I remarked on the quartz lamina?, small 

 brilliant, gold-coloured specks, precisely similar to those seen in the 

 auriferous quartz veins in the rocks of the Malabar coasts, specimens 

 of which have been deposited by my friend Colonel Cullen in the 

 museum of the Asiatic Society of Bengal. Does this appearance indi- 

 cate the existence of particles of gold in this ore ? We know that in 

 America, gold is occasionally found in the siderocrisfe, which is a spe- 

 cies of quartz iron ore, like the cne just described*. 



It is the belief of some people, that owing to the similarity of the 

 rocks, of the detritus, and of the quartz veins, of the Malabar coast, 

 and of these hills, gold may be found in this last, as well as in the for- 

 mer. The specimen of the earth I send is taken (No. 22) from an ex- 

 cavation made, some years ago, by an officer, who had been employed 

 on the Malabar coast, for the purpose of ascertaining the existence of 

 gold in the detritus of that coast. It is said that he found gold in the 

 earth dug upon the side of one of the hills of the Doodabetta group, fac- 

 ing the cantonmentf . 



Before concluding my observations regarding this magnetic iron ore, 



* The specimen of Colonel Cullkn is marked '■' auriferous quartz, stratified : Nelli 

 Allum, Malabar." The same gentleman sent to the museum another specimen, which he 

 calls " auriferous mica-schist," which contains the same kind of shining, gold coloured 

 specks. 



+ The sand which results from the disintegration of this species of iron ore is very 

 nearly similar to what is called titaniferous sand. — Does any menaccanite exist in this 

 sand ? The rock in which this ore is contained, appears to be similar to that which is 

 seen in Cornwall, from which the sand containing that new mineral is derived. Profes- 

 sor Sedgwick informs Mr. De la Beche, that the menaccanite of Cornwall is derived 

 from the decomposition of a hornblende rock, composed of hornblende and felspar.— Geolo* 

 gical Manual. 



