12 



HARDWICKE'S SCIENCE-GOSSIP. 



The diamond-bearing district of South Africa is, 

 as far as yet known, confined to the Vaal Valley, some 

 of its tributaries, and a part of the Orange lliver, 

 below its junction with the Vaal. For the most 

 part, the district of Colesberg, Albania, and Orange 

 lliver Free State (which include most of the dia- 

 mond-diggings) have the Karoo strata, or great 

 Dicynodon formation, that underlies so large a part 

 of the Cape Colony, for its basement, traversed in 

 every direction by dykes of greenstone and other 

 volcanic rocks. Along the Vaal River, however, 

 the Karoo beds, if they ever extended quite so far, 

 have been denuded off, leaving some schistose and 

 shaly beds, traversed by basalt and other volcanic 

 rocks ; and these may be either remnants of the 

 Karoo beds, or some of the palaeozoic rocks beneath. 

 Excepting occasional exposures, all these are covered 



Fig. 11. Diamond "Star of South Africa," face and 

 back as cut. 



with superficial deposits of tufa, pebbles, and sand . 

 The pebbles consist of rock crystal of various 

 colours, agate, jaspers (black, red, and ribboned), 

 quartzite, sandstone, iron-ore, basalt, granite, 

 garnet, spinel, peridot, blue corundum, and dia- 

 monds. Where the quartz is angular instead of 

 rounded, diamonds are said to be wanting. The 

 superficial sand and soil, generally ferruginous, and 

 even the tufa, have also been found to contain dia- 

 monds here and there. The diamond-bearing pebble- 

 bed is formed, not only on the flats along the river, 

 but also on the tops and sides of the hills (" kop- 

 jes "), sometimes one hundred feet and more in 

 height, within a few miles of the river. Most of 

 the pebbles have been probably derived from the 

 Quathlamba Mountains or Drackenberg range, 

 which has certainly in its constitution all the 

 materials for the common pebbles, and probably the 

 rarer minerals also. The strata that have before 

 now occupied the place of the Vaal Valley may have 

 yielded some of the material, slowly let down from 

 jevel to level, and pushed gradually forward, as the 

 strata were worn away by water through great 

 periods of time ; certainly the presence of the 

 pebbly accumulations on the kopjes indicates the 

 existence of former levels of water-worn deposits, 

 portions only of which now remain after the erosive 

 action of the rivers. These kopjes seem to be 

 harder masses of protruding basalt than the rest, 



and are said to have rich stores of diamonds re- 

 maining in the old alluvium coating their tops and 

 sides, but often hidden by sand drifted from 

 flats. The association of agates points of course to 

 volcanic rock, even if no basalt or greenstone had 

 been found ; and the abundant evidence of igneous 

 action, both in the Vaal Valley and in the water- 

 shed whence the river comes, may probably have 

 had to do with the origin of the diamond, in 

 changing coal or some other carbonaceous com- 

 pound into pure and simple crystals of carbon. 



The many papers in the Colonial and other pe- 

 riodicals, by Atherstone, Rubidge, Gilfillan, Higson, 

 Shaw, Muskett, Grey, and others, have been the 

 chief sources of this information concerning the 

 diamond fields collated for me by my friend Profes- 

 sor Rupert Jones. 



As in South Africa, so in Brazil and India, dia- 

 monds have been formed in superficial pebble-beds, 

 whether loose or conglomerated, containing quartz 

 and other hard rocks, derived probably from moun- 

 tains many miles away, of palaeozoic and highly 

 altered rocks. It is difficult, however, to make an 

 exact comparison of the pebbly alluviums, so rich 

 with diamonds, in these three countries. So also of 

 South Australia the same may be said ; and doubt- 

 less diamonds will be found under similar conditions 

 in other parts of the world. — Lecture at Society of 

 Arts. 



DARKLING SPIDERS. 



P\ID it ever occur to any naturalist that it is a 

 -^ rather singular circumstance that spiders 

 should spin their webs in closets or places which are 

 entirely dark ? For what purpose is the silken snare 

 spread by these crustaceans ? We naturally answer, 

 that its primary object must be to entrap winged 

 insects, yet totally dark places yield few of these. 

 Observe that I am speaking of spots where light is 

 not intermittent, but from which it is shut out for 

 months together. I have recently been making 

 some investigations relative to the habits of spiders 

 resident in a closet which is not opened for many 

 weeks at a time, situate on the basement of a house. 

 Within this a spider might well despair of getting a 

 good living, unless it had either capacities with 

 which spiders do not appear to be gifted, or pos- 

 sessed the art of subsisting upon other aliment than 

 that which we assume, with good reason, is that 

 which has been assigned them by Nature. 



What insect is likely to fly about in a dark closet ? 

 The chances of any entering at those rare intervals 

 when the door was open would afford a meagre 

 livelihood to any spider, even if these visitants, once 

 shut in, were likely to blunder about until they fell 

 into a snare ; but here were many spiders, and from 

 their appearance they showed evidently that they 



