J. R. Kili'oe — Laterite and Bauxite in German)/. 539 



Maclaren : " Lateritic deposits require for their formation («) tropical 

 heat and rain with concomitant abundant vegetation ; (h) alternating 

 wet and dry seasons." ^ Holland, too, assumed the necessity for 

 tropical conclitions when relying upon the intervention of bacteria for 

 the production of laterite. Whatever value may be attached to this 

 suggestion, it is freely admissible that the chemical processes involved, 

 organically, in the abundant growth and rapid decay of vegetation, or 

 in the inorganic reactions proceeding in the eai-th's crust, are greatly 

 stimulated by heat ; but are tropical or sub-tropical conditions 

 requisite ? The laterite (red clay) described by Mulf occurs at such 

 an elevation- in East Africa that heat could scarcely be claimed as 

 an essential condition for the peculiar alterations in question ; he 

 holds that the decay of forest vegetation — acids resulting therefrom — 

 is a chief factor in the transformations.^ 



The usual impressions regarding the necessity for tropical or sub- 

 tropical heat were in one's mind in going to Germany ; with this, 

 however, was my conviction that atmospheric carbonic acid, carried 

 into the earth by rain, played a more important part than the one 

 usually assigned to it if acting under favourable geographical and 

 climatal conditions. I have had to modify my convictions regarding 

 the necessity for heat, for the Vogelsberg laterites, etc., were 

 formed at the threshold of the Glacial Period, as has been 

 shown above, and my belief that C Oo played a very important 

 part has been strengthened. Abundant forest growths often 

 accompany deposits of laterites and bauxites, the decay of which 

 -\irould have given off quantities of this gas. But where no obvious 

 proof of former vegetation exists, as, in my experience, is the 

 ease in Hesse, C O3 issuing from fissures as a post-volcanic product, 

 as suggested by the carbonated springs at ^Nauheim and at several 



1 Geol. Mag., 1906, p. 546. 



• Some 9,500 feet. Op. cit., p. 42. If tropical heat were the determining 

 condition, should we not expect lateritic deposits everywhere throughout the tropics, 

 declining in importance northward and southward in the temperate zones, wherever 

 basalts, dolerites, etc., appear at the surface? Miinster, while questioning the 

 existence of tropical conditions during the formation of the laterites at Miicka, resorts 

 to thermal springs, with Chelius and Delkeskamp (op. cit., p. 257), as the effective 

 cause. The carbonated Avaters of the springs, he believed, brought up iron and bore 

 it into the laterite layer, as well as promoting the weathering of the basalt. As to 

 this I would remark — 



(1) The laterite layer, always superiicial (practically), occurs from 1 to 3 

 kilometres from the fault along which the supposed springs issued. Could the waters 

 have retained heat to such distances and have affected only a superticial layer of rock ? 



(2) The peculiar weathering has proceeded from above downward, the greatest 

 concentration of iron-oxide being at the bottom. Is this not analogous to the case of 

 iron-pans m soils on a larger scale ? 



(3) The amount of iron given up by the basalt, in weathering to clay in the upper- 

 most 20 feet, could easily account lor the aggregate of limonite deposited in the 

 lower 20 feet. 



(4) May not the C O2 given off by springs, such as those now at Nauheim and 

 along other lines of post-basalt dislocations, including that at Miicka, have been 

 carried into the earth from the atmosphere, and affect the rock more generally than 

 when issuing only at points here and there ? 



3 G. H. Kinahan relied upon the leaching action of the organic acids from 

 decomposing peat to account for the formation of bauxite. Trans. Manch. Geol. 

 Soc, 1894, vol. xxii, p. 458. This is mentioned by Clarke, op. cit.,. p. 420. 



