l68 Kezu Vithlicatiom. 



the nail of the finger, is called huX. hiduratcd earlh : if its 

 cohefion firmly refiit the aftion of the nail, it is to be deno- 

 minated a Jlone. Stones arc hard which cannot be eafily 

 filed, or cat inlo pieces. Thole are firm which ilrongly 

 refift percuflion. Some ftones appear to have been formed 

 by crydallidition arranging all their parts, internal and ex- 

 ternal, in a regular form. It is effefted from cither aqueous 

 or igneous fulution. All folidifiable matters are fufceptible 

 of it. Even thofe filiceous matters, which are now almoft 

 infoluble in water, might be eafily foluble in this menftruum 

 in their original ftate of extreme divifion, and were probably 

 cryftallifed by dcpofition from water. Nay, in fpite of what- 

 ever Black and others may have affirmed to the contrary, 

 numerous fafts may be produced to (how that, even ftill, 

 water may be made to take up a certain proportion of this 

 earth. Some ftones appear to have been formed by the mere 

 concretion of particles which in their primary compofition 

 are probably of different figures, and which therefore difplay 

 not in th^ir cohefion the uniform order of cryfiallifation. 

 Other ftones are formed by the cementation of exceedingly 

 fmall nodules, or even of larger ones, by the dcpofition of 

 ftill particles amongft them, and the cohefion of whole 

 mafles, partly by mechanical force, and ir part by the reci- 

 procal chemical attradions of the ditferent parts. Many of 

 the fmaller nodules, which are found imbedded in rocks not 

 of the fame nature \Aith therafelvcs, have I.)cen formed by 

 an infiltration, in which water or foine other fluid carried 

 their particles through the fuperficial ftrata, but dcpofitcd 

 them after penetrating the in erior layers only to a certain 

 depth. Thofe ftones which we call petrefaclions have been 

 formed by the gradual fubftitution of Itony particles into the 

 pJaces which were occupied by animal or vegetable matter^ 

 that decay while the lapideous dcpofition takes place. Thefe 

 are all the different modes of lapidification. They are ex- 

 emplified in ail the dif?(;rent fragments, columns, and ftrata 

 of rock which the earth prcfents to the obfervation of men. 



In the fifth Efliay, the dljintegratlon, reducing them into 



fands and larger fragments is explained, as having been often 



produced by the abforption of water, and by its congelation 



7 or 



