in tke Plastic Clay of Auteuil, near Paris. 83 



a white earthy substance at Bernon, near to Epernay, in the 

 lignite of that canton, M. Lassaigne analysed it, and found it to 

 be also a subsulphate of alumina, but differing somewhat in the 

 proportion of its constituents, owing probably to some impuri- 

 ties ; for it is proper to state that Websterite appears always 

 as a white friable earth, and that it is difficult to detach it en- 

 tirely from the clayey matrix which surrounds it. 



But it is a singularity in this mineral, which I have con- 

 stantly observed in the three examples just mentioned, that it 

 is composed of an infinity of minute acicular crystals, so small 

 that they cannot be seen without a microscope with a magni- 

 fying power of at least 400 times : then the crystals are very 

 distinct. M. Schreiber had remarked them in the Websterite 

 of Halle : I found them in that of Newhaven and Epernay ; 

 and by means of the fine microscope of Amici, I have been 

 enabled to determine that they consist of six-sided compressed 

 prisms terminated by two culminating facets, consequendy 

 having a form incompatible with that of alum. 



The three examples of Websterite found in places very di- 

 stant from each other, possess therefore the two classes of 

 characters which essentially constitute mineral species, parti- 

 cular composition and form. Let us now examine their geo- 

 logical situation ; and this will not be a useless repetition, 

 since we may thus avoid describing the same circumstances 

 in detail, when speaking of the Websterite of Auteuil. 



The Websterite of Newhaven has shown clearly the geo- 

 gnostic position of this mineral : it is there in nodules of from 

 one inch to two or three inches in diameter, imbedded in an 

 ochrey clay mixed with gypsum, which is placed upon the chalk, 

 and which penetrates in irregular veins the superior and dis- 

 integrated part of the rock. That of Bernon, near Epernay, 

 found by M. Basterot, occurs also in veins and nodules, in 

 the plastic clay above the chalk, accompanied by lignite and 

 gypsum. 



If, after having acquired these ideas respecting the position 

 of Websterite in two points more than 100 leagues asunder, we 

 should extend our observation to Halle in Saxony, 200 leagues 

 further, we shall there find, instead a supposed ordinary allu- 

 vial soil, the plastic clay with its gypsum, its lignites, its am- 

 ber, and its Websterite disseminated in nodules through the for- 



gcntleman inserted a notice respecting it in the Journal de Physique^ for 

 September 1814. Previous to that time all the knowledge respecting it in 

 England, seemed to be confined to the notice of the substance found at 

 Halle, and which was described in our elementary books as native alumine. 

 — Edit. 



M 2 , mation. 



