S A Repy to 3/r. Pltrjfair's R^feSlions en 



underfland; but that f^nd is fometimes found rep;ularly cryf- 

 tallized is evident, for a whole ftratum of fuch faiul has been 

 found at Neuilly : to expeA that a fubftance expofcd to cnd- 

 lefs fri(5lion fliould always be found in regular cryflals would 

 be extravagant; that of Neuilly was therefore formed on the 

 fpot in which it was found. — A vein filled with fand has been 

 fcnind among the mines of Peregruba in Siberia. Renovantz, 

 Preface, xiii. Gravel and fand differ only in fize, and to 

 expeiB either in granite rocks would be inconfiftent; but oa 

 and befide granitic mountains grave! very frequently occurs. 

 The cryftallization of bafalts is fo far from being afccrtained, 

 that, on the contrary, it has been demondrably proved that 

 bafaltic prifms are not cryftallized, by thofe that have paid 

 moft attention to this fubjeft. — Rome de Lifle, i. p. 439; 

 Haiiy Miner, iv. 476. 



Page 180. " The Neptunift, who has provided the means 

 of diltblving the materials of the ftrata, has only perlorrned 

 half his work, and mud: find it a tafk of equal difficulty to 

 force this powerful menfiruum to part with its folution. Mr. 

 Kirwan, aware, in fome degree, of this difficulty, has at- 

 tempted to obviate it in a very fingular way. Firft, he afcribes 

 the folution of all fubflances in water, or in what he calls 

 the chaotic fluid, to their being created in a ftate of the moll 

 minute divifion. Next, as to the depofition, the folvent be- 

 inir, as he acknowledges, very infufficient in quantity, the 

 precipitation took place (he fays) on that account the more 

 rapidly. If he means by this to fay, that a prccipiiation 

 without folution would take place the fooner, the more in- 

 adequate the menftruum was to diffolve the whole, the pro- 

 pofition may be true ; but it will be of no ufe to explain the 

 eryftallization of minerals (the very obje<Sl he had m view), 

 becaufe to crvliallization it is not a bare fubfidence of par- 

 ticles fufpended in a fluid, but it is a paiTage from chemical 

 folution to non-folutioQ or infolubility that is required," 

 . My meaning is clearly ftated in pages 10 and 11 of my 

 Geological EflTays, that the folids conUnned in tlic chaotic 

 fluid were not diOblvcd by that fluid, but were contained in 

 that llate of minute divifion to which, if the fluid could of itfelt 

 diflblve them, they would be reduced ; and that, if the quan- 

 tity of that fluid were infuflicient to hold them in folution, 

 this circumltanct. would haf^en their cryftallization, precipi- 

 tation, and depofition, refpcftively. I did not aflert that the 

 folution was elfecTcd by the mrnflruum, but, on the con- 

 trary, denied it. Mr. Playfair's aflertion, that cryftallizaiion is 

 a pafl'agc from chemical folution to non-ibkuion or iulolu- 

 ^ility, is denied by Bergman : " Scd mn tanlum vcre Jolufa, 



in 



