406 H. C. Sargent — Clay-hands in the CricJi In Her. 



per gallon) and organic matter, together with insufl&cient inorganic 

 radicles to satisfy the basic radicles. This water apparently contained 

 organic compounds of iron. 



Alumina is present in all the laterites, hut most abundant in those 

 overlying granite and other less ferruginous rocks. In the Wongan 

 Hills and Smith's Mill samples it appears to exist as gibbsite, 

 AI2 O3 . 3 Hj 0, in other cases it is less hydrated, corresponding to 

 bauxite, Al.jO3.2H2O, or diaspore, AloOj.HjO. 



Titanium oxide is always present in appreciable amounts, probably 

 in the form of metatitanic acid, Ti Oo . x Hj 0, for which no 

 mineralogical name has yet been suggested. Experiments on the 

 Coolgardie laterite showed it was not present, except in traces 

 perhaps, as rutile or ilmenite. The titanium compound was found 

 to be insoluble in warm dilute hydiochloric acid but soluble in fuming 

 sulphuric acid. 



Silica is present as (1) quartz, or rai'ely felspar, mechanically 

 entangled, and (2) in combination in a form decomposed by strong 

 hydrochloric acid, probably halloysite. 



Only very small percentages of manganese oxide have been 

 observed. 



Chromium oxide has been detected in every case where it was 

 looked for. It varied from a trace to 5 "30 per cent. In the latter 

 case it was almost wholly present as chromic hydrate, soluble in 

 strong hj-drochloric acid. A small proportion was present as chromite. 

 It is probable that where the percentage of Crj Oj rises above O'l per 

 cent the underlying rock is of an ultra-basic type. 



Notable amounts of vanadium were detected whenever looked for. 

 The highest proportion noted was 0-65 per cent,V.2 05(?), in a turgitic 

 laterite from Xalgoorlie. The form in which tliis constituent occurs 

 in the rock is not yet determined. This is only one of many unsolved 

 problems connected with this deeply interesting formation. 



IV. — On the origin or certain Clay-bands in the Limestone of 



THE CrICH InLIER. 



By H. C. Sargent, F.G.S. 

 Litroductory. 



11^ the Carboniferous Limestone of the Crich inlier in Derbyshire, 

 there are numerous clay-bands or partings interbedded with the 

 limestone which appear to throw considerable light on the geological 

 history of the area. 



These clay-bands vary in thickness from about 3 feet down to the 

 thinnest possible parting between two beds of rock. Some of those 

 between the higher beds are undoubtedly contemporaneous detrital 

 sediments ' and appear to indicate shallow-water conditions ; others, 

 though consisting of sedimentary material, were probably deposited 

 along solution planes subsequently to the formation of the limestone; 



' Many, perhaps all, of the tuffs of Derbyshire are sediments, but, to avoid 

 ambiguity, the use of the word in this paper is confined to detrital deijosits, the 

 waste of a land-surface. 



