284 TlMEHRI. 
Turning now to the discovery of diamonds on the 
Massaruni River, we find the locality in question 
distinguished by a formation somewhat different from 
the ordinary gold drift. BURTON describes the mate- 
rial of the San Joao mine as a hardened paste of clay, 
whose regular and level stratification argues it to have 
been deposited in shallow water. The eastern side 
is the more ferruginous formation, on the West it is 
mixed with beds of white sand. Below one foot of brown 
soil, the argillaceous matter has the usual staining and 
marbling, glaring-white like fuller's earth with felspar 
and kaolin, or of different tints from organic matter, 
oxides of iron, copper, manganese, etc. The diamon- 
diferous soil of the Massaruni may be described in 
similar terms ; it consists of a peculiar fat-white clay 
composed of kaolin or decomposed felspar, overlaid with 
the gem-bearing gravel of fragments of variously coloured 
quartz, rock crystals, white sapphires, and other crystal- 
line minerals. Over a large portion of the Upper Massa- 
runi Valley, there occur extensive beds of recent gravel 
and sand, touching whose origin the theory of Mr. HlLL- 
HOUSE may be of interest. Remarking that the smooth 
expanse of water above the fallen rocks at Teboco cata- 
ract presents the appearance of a lake, rather than of a 
river, he observes that, " if at a more or less remote 
epoch the horizontal stratum of granite at Teboco had 
been perfectly compact and unbroken, the water must 
have stood at least fifty feet above the present level, and 
there would thus have been formed an immense lake 10 
or 12 miles broad, and 1,500 to 2,000 miles long." The 
characteristics of the level land between the river and 
the base of the sandstone mountains are very suggestive 
