16 ANNIYEESARY ADDRESS. 



It seems that tlie diamonds are now found either on- the 

 surface or at a depth of from 3 to 7 feet, from which depth 

 all the large ones have been obtained. 



At Du Toit's Pan the most common depth is from 5 to 9 feet ; 

 but diamonds occasionally, and rarely, occur at 30 feet. Some- 

 times they are broken from concussion, — sometimes with chipped 

 edges, — and in the river beds are water-worn and unabraded. 



The average yield per cubic yard is diiEcult to assign ; but in 

 one place 35 loads of surface sand yielded fifteen diamonds, of 

 average weight each 8 carats. Underneath this, a hole 1,280 

 cubic feet in extent produced nine diamonds, weighing in all 6| 

 carats. 



As affording some distinct idea of the geological character of 

 the country from Cape Town to Pniel, Mr. Dunn gives the 

 following order of succession : — 



First, 70 miles Lower Silurian rocks ; 35 miles of sandstone — 

 Devonian or Vjppcr Silurian — neiver than Table Mountain. (I am 

 glad, in this statement, he confirms my view of the age of the 

 rocks about Table Mountain, as they appeared to me in my 

 exploration of them in 1839). Next, 5 miles of trap conglomerate 

 or hreccia, filled with boulders of granite, gneiss, mica schist, 

 porphyry, sandstone, jasper, slate, &c. Then 65 miles of slaty 

 sandstone, with fresh- water and land plants, &c. Next, 115 miles 

 of lower dicynodon beds, with huge fossil saurians ; 210 miles 

 upper dicynodon beds, full of igneous dykes and beds. These 

 also are full of fossil saurian and vegetable remains. " On tTiese 

 are situated our present diamond fields of South Africa." 



It is nevertheless remarkable that, as in Bahia, a gneissic rock 

 appears to be the base of the diamond region, but it is by no 

 means clear that it is of the same class as the Brazilian rock. 



Professor Jones demonstrates some agreement with what is 

 known of Bahia, and also some peculiarities of a different kind, 

 such as sandstone not tertiary, as I believe, underlying the trap 

 and resting on schists. 



