1813.] Scientific Intelligence. 237 



hitherto ignorant of the true repository of diamonds. Werner, 

 indeed, conjectured that they occurred in the rocks of the newest 

 floetz trap formation ; but this conjecture was not supported by 

 any direct proof. Dr. Benjamin Heyne, botanist and naturalist 

 to the East India Company at Madras, has lately brought over 

 to London a piece of the diamond bed at Banaganpally, in the 

 Dekan, with a diamond actually imbedded in it, from which we 

 are enabled to determine the nature of the rock with tolerable 

 accuracy. As it is perhaps the first specimen of the kind brought 

 to Europe, mineralogists will doubtless consider it as of some 

 importance to present them with a description of it. To the eye 

 it has the appearance of a conglomerate ; but as the grains are 

 commonly roundish, and the cement a clay, approaching to 

 wacke in its appearance and nature, it seems rather entitled to 

 the name of amygdaloid. The round grains of which it is 

 composed are chiefly of chalcedony, of ablueish grey colour, and 

 approaching a little to hyalite in their appearance. They vary in 

 size, from a pin head to a hazel nut. These nodules are mixed 

 with angular fragments of jasper, hornstone, and quartz. No 

 fragments of corundum were visible; though, it is said, they 

 now and then occur in some of the beds containing diamonds. 



From the above description there can be little doubt that the 

 rock in question is an amygdaloid belonging to the newest 

 floetz trap formation. Though the nodules are not absolutely 

 identical with those which occur in the amygdaloid of this 

 country, yet they very nearly agree with it. 



From Dr. Heyne's description, it would appear that though 

 this amygdaloidal rock is of some considerable thickness, yet 

 the diamonds are confined to a bed in the centre of it, not more 

 than a foot thick. This bed is distinguished from the rest of the 

 rock by being harder. 



IV. Carbonate of Iron. 



It has been known for some time to mineralogists that the 

 substance called sparry iron ore, and jlos Jerri, is a compound 

 of black oxide of iron and carbonic acid, or a carbonate of iron , 

 and Dr. Wollaston has shown that it crystallizes in a form differ- 

 ing a little from that of the primitive crystal of calcareous spar. 

 It h.ts lately been determined, by the chemical analysis of 

 Dcscotils, and several other chemists, that the species known by 

 the name of clay iron-stone, and so much employed in this 

 country as an iron ore, is in fact a carbonate oj iron likewise, 

 and differs in nothing from sparry iron ore, except in not being 

 tallized, and in being mechanically mixed with some sili- 

 i mils matter and some manganese. Alumina is usually present 

 only in a very small proportion, and seems to be in combination 

 with the silica; though in some specimens the proportion of 



