
          he was mistaken in supposing he had another
 letter. The letter was inclosed in the parcel.


 How am I to distinguish Graywacke from Greenstone
 or from Conglomerate. I suppose the division very arbitrary. 
 I should like to have a well marked
 specimen of it and another of Graywacke slate.
 I send you a few pieces of a rock very common in
 this neighbourhood in rolled pieces which is made
 up of grains of the size of peas or less cemented by a 
 substance more liable to disintegrate. The [added: little globular] masses
 have [faults?], are compact, melt without great difficulty
 into a black Glass, in all which characters they resemble
 Coccolite but they differ in appearance looking
 very like Basalt and [are?] scratched by the knife. When
 the cement does not disintegrate, the grains are less distinct
 & [added: it] appears sometimes nearly compact. I do not
 find any account of such a rock in the books: it might
 be a puddingstone if the grains were of other matter.
 Indeed it is here called plum puddingstone. Altho
 I do not think it Coccolite, I should like to know some
 distinguishing character besides that fallacious one of
 color. While talking of distinctions, what decisive
 characters distinguish Augite, since it is white & black
 & melts into white & black Glasses. Really it is perplexing.

        