Recent Formations. 



lOi 



fragments, and with, in many places, layers, boulders and nodules 

 of concretionary ironstone. The titaniferous iron-ore, present to a 

 considerable extent in the diabase and allied basic rocks, undergoes 

 but little alteration by weathering, and is found in the earths in the 

 form of black sand. One of the surest signs on the rivers of approach 

 to an area of basic rocks is the occurrence in quantity of l)lack sand 

 among the river sands and gravels. 



The clay produced from the basic rocks varies in depth of colour 

 according to the quantity and composition of the ferro-magnesian 

 minerals j^resent in the rocks ; those rich in iron compounds giving rise 

 to deep-red and chocolate-coloured clays, while those with less amounts 

 result in i-ed, light red, or ochreous clays and earths. The surfaces of 

 these claj's are not unfrequently more or less bleached bv the action of 

 the organic acids present in the percolating waters of the soils of the 

 forests, and frequently, where the surface-soil of the forest has a light 

 colour and gives no indications of underlying basic rocks, the earth 

 thrown up from the tunnels of armadilloes and other burrowing animals 

 is of a red or deep-ochreous colour, showing the presence of the 

 characteristic degradation-products of the basic rocks. 



In many places the bulk of the laterite consists of very finely 

 divided particles, and is there very absorbent of water. Earths of this 

 character, when saturated or nearly saturated with water, in place of 

 becoming plastic and tenacious, as true clays do, approximate in 

 character to viscous liquids, transmit hydrostatic pressures, and, as on 

 the slopes of hills, flow more or less freely under the influence of 

 gravitation. To this may be ascribed the formation of the numerous 

 small faults which characterise the layers of quartz found in the 

 laterites of the Arakaka district ; whilst, as will be shown later, these 

 properties explain to some extent the concentration of gold, of quartz 

 and ironstone in the lower layers of certain of the laterites. 



The folloMang analyses indicate the chemical composition of the 

 laterite deposits : — 



