[ si+M

f varieties, take us four times the room and numbers they ought to do. -Pebble crystal, be-cause often orbicular in form , is rangd among these also. Flint and the Agates , and otherfemi-pellucidGems, to: which be has allow’d no proper Germs, confuse also , and swell up thaccount ; and befide etll these, the fame Pebble is defcrib’d m one-place plain, and in anothermark’d withfreaks, as they are call'd ; which every' one, who has loosd into nature withany degree of care, must be amaxd, that the author did not know to be extraneous bo-dies of the Coral kind, accidentally lodg’d in the stone-, and no more altering its nature,than the fells in clay pits the flratum in which they are buryd.. Another considerable ad-dition to this class is also from small masses of ' (lone broken from strata of different kinds,and properly reducible to .that class, and to their severalspecies, with great :eafe', by an or-dinary inspector, on comparison of their ftruchtre when broken, with that of the severalflones or jirata. > ■

With these, and many other additions like these, it is no wonder, that a catalogue ofspecimens of Pebbles , might he brought up. to a larger number, than even this author’s book,or the nicji numerous collection among us at present amounts to-, and without these, howgreatly mujl they be reduc’d ! and how small, in comparison' op this, muf be the numberallow’d by the per Jon, whose business it is to reduce varieties to their proper species, anddescribe in other places , .and in their proper genera, all the flones not properly Pebbles,which are there call’dso. \ \ . . : t . .

. On these principles .the reader.wiU not wonder to find the Pebbles of the whale-world,' (ispar as they have hitherto come to our knowledge^ here, included in no great number if species,tho ’ Dr. Woodward alone accounted he had Jour hundred. Far be it from me to censurethat excellent writer, notwithflandmg ail hissaults,'either thro’ the ill natur'd and dijhonejlpleasure of degrading others, or the pride op' improving: on him ; what I. am oblig'd, inconsequence of my own attempt, to observe in regard to the errors op some parts of his wri-tings, juplice to mys elf will not permit me to omit. Ache world, who have very deservedlya great ejleemfor what he has left us, would naturally wonder at the great diff erence inour accounts of the fame things, unless :it were explain d why we differ, andso far aloneshall I be pound touching upon his errors, .elsewhere it will ever be my pleasure to allow

him the honour he deserves. :s '

* * • ' -

The natural formation of Pebbles, is Sy incrustation from the additions of fresh matter,at different times, in form of so many ' coats round a firjl fornid central Nucleus • but iffthe fame matter be dij'pos’d in a different order, or even if the Nucleus appear wanting, -byits being blended among the other matter of the jlonc, we are not to call the Jlone a differentspecies for that reason, but a variety okly of that which, in other in/lances, we find with ■<*Nucleus, and form’d of crisis ; the absence of the Nucleus indeed, in its -proper form, is thegreat, reason of all this'variation, flnee the fame matter which, by being dij'pos’d regularlyround it, would have p'orm’d crisis, or concentric circles, mujl, when it has no such fix’dpoint to be form d upon, either absolutely blend together into one mass of a mix’d colour,or be subjeSt to thesame. laws with the matter of the Agates, and have its variegationsdifpos’d in the j ame .order.:. And thus we fee the variegated Pebble-without Nuclei eveswithout the regularity of the. concentric circles also, and ever emulating theplruSlufe opthe Agates. ‘ '

I. Calculus grifeo ftavefc-ens , crufia alhido fubcœrulea.

Yelkwijh grej PeBhhy with a Bltieijh vbhite cruft.

T HIS is- of an extreamly pure, fine, close and compact texture, of a tolerably re-gular and equal, but wrinkled surface, generally approaching to an orbicular or ob-long figure, and in size, from one to four, five, or six inches in diameter; it is usuallycompos’d of a very large central Nucleus enclos’d in one broad crust, and that co-ver’d with a very thin coat. Its Nucleus is of a greyish yellow; these colours sometimesare very equally and perfectly blended, and make a plain third colour between them, but,more frequently they are irregularly mix’d in form of clouds, or large spots, either of yel-' low in the grey, which is most usual, or sometimes of grey in the yellow j and often thereare whitish opake spots dispers’d here and there visible among them ; the substance ofthis Nucleus very nearly approaches to the nature of pure Flint, differing from it in-deed in nothing hut the addition of the yellow earth that makes the variegation, andwhere it is free from it appearing plain and pure Flint; the crust including this, is of ablueish white, and of a somewhat coarser texture, being more debas’d by earth; this