452 Dr. Boase's Inquiry into the Nature 



beads, the molecular, concretionary, and jointed structures, 

 thinking that there was evidence of these three stages suc- 

 ceeding each other during the consolidation of rocks. It 

 was then also stated that stratified rocks formed from sedi- 

 mentary deposits, possessed, when solidified, similar structures, 

 effected by the same cause, viz. the agency of the attraction of 

 aggregation. The first stage of consolidation is already ac- 

 complished in deposits of sand, gravel, pebbles, and the like ; 

 for the molecules are united into distinct bodies : these, in the 

 next place, are combined into various concretional forms, such 

 as nodules, spheroids, angular and venous portions, and, per- 

 haps, laminae and slates, though these last are so intimately 

 connected with the jointed structure that I am not inclined 

 to separate them from it. And it may be here remarked, 

 that as the joints, in igneous rocks, sometimes traverse large 

 crystals formed during the first or molecular stage, so in 

 some sedimentary rocks they occasionally intersect the pre- 

 viously existing pebbles and fragments of which these rocks 

 are composed. 



On this view of the subject, no distinction is attempted be- 

 tween laminae that have different positions as regards the beds 

 or layers in which they occur, nor between those which be- 

 long to rocks of various origin. And whilst the slaty cleavage 

 and the joints are referred to the same crystalline action, yet 

 it is not denied that the rocks may have been subject to rents 

 and fissures by mechanical violence ; but if thus disturbed, 

 it is presumed that the continuity of the rock would be 

 broken in directions parallel to the crystalline planes or joints 

 in preference to any other, as offering least resistance ; thus 

 the structure of the mass may be more clearly displayed ; but 

 its origin need not be attributed to such convulsions. To 

 sum up the whole, " it matters not whether a consolidated 

 rock has had an igneous, aqueous, or any unknown origin ; 

 its particles were once disunited or mobile, either by the re- 

 pulsive agency of caloric, by chemical solution or suspension 

 in water, by mechanical attrition, or by some other cause: 

 subsequently, however, its particles have been brought within 

 the sphere of their mutual attraction by a reduction of tem- 

 perature, by precipitation, by great and long-continued pres- 

 sure, by the percolation of water imparting the requisite de- 

 gree of motion, or introducing extraneous matter by which 

 the particles are cemented, or lastly, by any two or more 

 compatible causes which can operate in unison to effect the 

 cohesion of its particles." 



Before concluding, permit me to make a few remarks on a 

 portion of the Professor's paper in which he has offered some 



