228 ANNUAL OF SCIENTIFIC DISCOVERY. 



the influence, of running water prior to the last great changes 

 which formed the present landscape. The greater number of 

 the water-worn pebbles and boulders are of the basalt of the 

 Kopjes. Many of them are crystalline sandstone, others are 

 water-worn fragments of clay-slate, sandstone, etc., of the sedi- 

 mentary rocks which exist in the Kopjes. The agates, tourma- 

 lines, and garnets are undoubtedly from some superincumbent 

 conglomerate sandstone which has yielded to denudation and no 

 longer exists at Klipdrift, and also to a considerable extent from 

 the amygdaloidal trap everywhere prevalent. I have in my pos- 

 session from the Vaal a single fragment of red sandstone contain- 

 ing garnets, but I have not succeeded in tracing this to its source. 



" It will, therefore, be sufficiently apparent that there must 

 have existed, at a remote geological period, a series of metamor- 

 phic and sedimentary rocks which lay above the present rock sys- 

 tem of the region, and that, through successive disturbances and 

 persistent denudation, these have been worn away, forming in 

 great part the alluvial soil of the present surface. In some few 

 spots remnants of this series still exist, as in the clay-slaty crys- 

 talline sandstone of some of the Kopjes now worked for dia- 

 monds, and generally in the fragments of sedimentary rocks 

 scattered over the surface along the whole Vaal Valley. 



" I am decidedly inclined to think that the diamonds have not 

 been washed down from some higher region. I hope to show, in 

 another article, that the Free State possesses an independent dia- 

 mondiferous centre, and that there no river has existed at any 

 time, for there is no evidence of water-wearing, and the soil is 

 not alluvial. Diamonds have been discovered 2 hours' distance 

 from Potehefstroorn, and all down the Vaal to its junction with the 

 Orange River, and thence to 10 hours' distance below Hope 

 Town. This is a stretch of at least 500 miles. I believe the 

 diamonds have come from some rock which may now have 

 vanished, but which existed formerly throughout the whole re- 

 gion. " Nature, Nov. 3, 1870. 



LAURENTIAN GRAPHITE OF CANADA. 



In the Journal of the Geological Society, for 1869, Dr. Dawson 

 publishes a paper, in which he sustains the view that the graphite 

 of the Canada Laurentian is of organic origin, and shows that the 

 amount of " graphite in the Lower Laurentian series is enor- 

 mous." A limestone in the town of Buckingham on the Ottawa, 

 which is 600 feet or more thick, with some 3 intercalated bands 

 of gneiss, is in some parts one-fourth graphite, and the whole 

 is not less than 20 or 30 per cent, graphite. In the adjoining 

 township of Lochabar, a baud of limestone 25 to 30 feet thick is so 

 reticulated with graphite. that it is mined for it ; and another bed 

 in the same district, 10 or 12 feet thick, yielding 20 per cent, of 

 the pure material, is worked. It occurs in equal abundance at 

 other horizons through beds of limestone, which have, according 

 to Logan, an aggregate thickness of 3,500 feet. In view of 

 the facts Dr. Dawson adds: "It is scarcely an exaggeration to 



