542 J. II. Kilroe — Laterite and Bauxite in Germany. 



the shaken siliceous compound after some of the alkalies, alkaline earths, 

 iron oxide, and alumina have been withdrawn as sulphates. Again, 



X + z R'o Ro (S 0^)^ + i? C Oo + !Z H.. ;i± 



r Si O3 (O'Ho). + s (AI3 0.3, « H.,) + u E'o C 0.. + r 11" C O3 + F, 

 where JT represents the still more shattered compound. 



Here now we have colloid silica, which will dissolve in an 

 abundance of the newly formed alkaline carbonates, and either entirely 

 disappear or become diffused through the mass perhaps to form 

 secondary quartz ; and free alumina, to form perhaps its unstable 

 carbonate, say when the supply of C Oo is abundant, and precipitate, 

 when that supplj^ slackens, as well as to go afresh into solution when 

 the supply again increases. 



If we suppose H, S 0^,, formed from pyrites in the rock, as suggested 

 by Hayes ; or, as suggested by Professor Cole, from post- volcanic 

 vapours — present, say, in such small quantities as not to be injurious 

 to vegetation — this acid would have been likely to initiate the attack 

 upon the silicates. The molecular constitution of these compounds 

 having been thus shaken or disturbed, the remaining substance, made 

 up of constituents in a nascent state, would have been laid open to 

 further attack, and probably wholesale solution as shown above, by C O3 

 in abundance, in rain-water carried down from a heavily charged 

 atmosphere : in this regard, Maclaren suggests, would the conditions 

 diifer from those under which common clays are formed, namely, those 

 in which C Oo is small in quantity and consequently weak in action.' 

 The conditions also differed from those in which kaolinization of granite, 

 etc., takes place, by the action, as H. Rosier shows, of thermal springs 

 and vapours.^ The alkalies, Mg 0, Ca 0, and Alo O3, it is believed, 

 would all be attacked and in time go into solution ; and, wherever 

 the acid became satisfied, the nascent Si Oo would become dissolved 

 by the alkaline carbonates — present, we may suppose, in large 

 quantity. Thus would the delicately balanced state be reached in 

 which, while capillaritj- is maintained in free play, a large quantity 

 of Si Oo might be carried off or be deposited at certain points, according 

 as the solution remained alkaline or became acid ; and the alumina could 

 be transferred from point to point throughout the weathered mass to 

 concentrate in bauxite above ■' or in the interstices of lithomarge below. 



Replying to queries of mine regarding the possibility of accounting 

 for the Vogelsberg bauxite by supposing the former existence of forests 

 in the region, or decaying vegetation yielding humous and carbonic 

 acids, Dr. Schottler has sent me the following note, November 9, 

 1908, viz. : " TJnsere Bauxite liegen vielmehr stets an der Oberflache ; 

 auch sind keine Anzeichen dafiir vorhanden, dass er sich unter einer 

 dichten Vegetationsdecke oder unter Waldbestand gebildet hat. 

 Ebenso hat man noch nie versteinertes Holz in dem Ton vom roten 

 Hang gefunden. Verkieselte Hiilzer kommen nur als Seltenheit hie 

 und da im Tuff vor." 



1 Geol. Mag., pp. 539-40. 



- Zeitschr. fiir Prak. Geol., 1905, p. 333. Paper by 0. Stutzer ia which he gives, 

 with approval, Rosler's view. 



^ Liebrich, op. cit., p. 96. The author believes that AU O3 was dissolved out of 

 the rothen Hang clay and concentrated in crevices, etc., of the bauxite lumps, as 

 hydrargillite. 



