THE 



PHILOSOPHICAL MAGAZINE 



AND 



ANNALS OF PHILOSOPHY. 



[NEW SERIES.] 



AUGUST 1828. 



XII. On Webster it e found in the Plastic Clay of Auteuil, near 

 Paris. By M. Alexandre Brongniart, Member of the 

 Royal Academy of Sciences, and Professor of Mineralogy at 

 the Jardin du JRoi, Paris.* 



HPHE occurrence of the same geognostic circumstances, in 

 •*■ districts considered to be of the same formation though 

 situated very remotely from each other, exhibiting even in the 

 beds least developed, a repetition of the most minute particu- 

 lars, — presents a phenomenon that cannot but attract the at- 

 tention of naturalists ; and appears to point out, that causes, 

 simple, but powerful and general, have concurred in produ- 

 cing the several strata deposited in each successive epoch. 



These reflections have followed from a discovery I have made 

 in the environs of Paris, of a substance which, in itself, is com- 

 paratively of little importance : but it is precisely because the 

 beds in which it is found are so feebly and irregularly developed 

 as scarcely to be entitled to rank as a formation, and because 

 this substance, occurring in small nodules, is possessed of cha- 

 racters not very important when taken separately, that we are 

 struck with its appearance in so many places situated widely 

 apart. 



We are not surprised at finding granite of similar composi- 

 tion in Europe, Asia, and America : but it is more singular to 

 observe Websterite always in the same formation in Germany, 

 England, in several parts of France, and even at the gates of 

 Paris. 



The mineral substance which forms the subject of the present 

 communication, is the subsulphate of alumina, which was found 

 first at Halle in Saxony, and which had been long known by 



* Extracted from the " Annales des Sciences Naturelles" for March 1828. 

 New Series. Vol. 4. No. 20. Aug. 1828. M the 



