2S6 TlMEHRI. 
chalky grit, a sort of calcareous tufa, or concretionary 
limestone, a mode of occurrence very common in South 
Africa, and in some of the Indian fields. I have not 
visited the spot where it was obtained, but I have seen 
specimens of some of the rocks from that part of the 
country, which consisted of the above-mentioned sub- 
stance, shale, sandstone, fine sandy conglomerate, black- 
ened and scorified as if by the injection of molten matter 
such as BURTON describes, with pebbles of varied compo- 
sition, while the loose sandy matter was identical in 
appearance with a specimen of diamondiferous sand 
from California exhibited in the Museum in Georgetown. 
Taken in connexion with the comparatively frequent 
discovery of diamonds in our placers, the subject is 
worthy of investigation, and legislation having already 
been provided for diamond mining, there appears to be a 
fair held open for the investment of capital. 
Several early writers on the colony have alluded to the 
existence in the interior of pebbles of singular colour and 
formation, and special mention has been made of certain 
hard lustrous crystals known as Marowini diamonds, but 
I am not aware what particular mineral was thus desig- 
nated. Graphite, it may be mentioned, which is closely 
allied to the diamond in composition though its origin is 
probably not the same, is abundant on the Barima and 
the Massaruni. but it is doubtful if it is of sufficient purity 
to be of economic importance. Sapphires, as already 
stated, have been found associated with diamonds, and I 
have seen some small specimens of the amethyst; while 
jasper, agates and rose and opalaceous quartz which 
could be used for jewellery, are abundant. It is not 
improbable that the opal may also exist, and in the 
