360 Analysis of Scientific Books and Memoirs. 



later epoch, instead of silcx, carbonate of lime was precipitated, together 

 with more or less of micaceous sediment, producing the satcharoidal lime- 

 stones. Upon this mica-schist, and graduating, into it, were deposited in 

 turn, as the waters of the ocean cooled, and its local disturbances ceased, 

 or recommenced, other stratified rocks, composed sometimes of a mixture, 

 sometimes of an alternation, of precipitated, sedimentary, and fragmenta- 

 ry matter, giving rise to the transition formations. 



In this manner was formed the first crust or solid envelope of the globe. 

 But beneath this crust a new process had now commenced, occasioned by the 

 increase of temperature and of expansive force of the upper granite beds; 

 which, having been greatly reduced in temperature by the dilatation it had 

 endured, and the partial vaporization of the water it contained, now be- 

 gan to receive an accession of caloric from the more intensely heated nu- 

 cleus. The first effect of such an increase in the expansive force of this 

 zone, opposed as it was by the increasing pressure of the strata, whose pro- 

 gressive deposition was going on above, would be to consolidate the inter- 

 mediate bed of gneiss ; the next, to produce, sooner or later, the disrup- 

 tion of the solid crust, which impeded its actual expansion. This result 

 took place on those parts where accidents of texture or composition in 

 the oceanic deposits led to them to yield most readily ; and in this man- 

 ner were formed, in the primeval crust of the earth, those original and deep 

 fractures, through some of which (fissures of elevation) were protruded 

 portions in a more or It ss solid state of the inferior granite, together with 

 replications of the foliated rocks, (as described in a former chapter ;) 

 while others (fissures of eruption) gave rise to local extravasations of the 

 heated crystalline matter in the form of lavas, that is, still farther lique- 

 fied by the greater comparative reduction of the pressure they supported. 

 By these partial elevations of the superficial strata, violent movements 

 were at times, as has been mentioned before, communicated to the waters 

 of the ocean which broke up the projecting eminences, and distributed 

 their fragments in conglomerate or sedimentary strata. At first, the sur- 

 face of the globe consisted chiefly of mica-schist ; and hence mica and 

 granular quartz predominate in the earlier conglomerates and sedimentary 

 strata, (grey-wacke, grey-wacke slate, quartz-rock.) Precipitations of silex 

 and carbonate of lime, continued to mix with the sediments of this pe- 

 riod, and Mr Scrope supposes quartz rock and transition limestone to owe 

 their dark colours to admixture with the finest particles of mica. For a 

 long time, it is probable that local developements of subterranean expan- 

 sion, producing partial elevations of the earth's crust, local extravasations 

 of crystalline rocks in the form of dikes, beds, &c. and local deposits of 

 conglomerate beds, alternated with periods of comparative tranquillity, 

 during which the finer sedimentary deposits and precipitations took place, 

 and hence the alternations of the various sedimentary and arenaceous stra- 

 ta which compose the secondary formations. Meantime, as the tempera- 

 ture of the ocean decreased, it began to be thickly peopled with organic 

 beings, animals, and vegetables of simple structure ; the latter giving rise 

 by their carbonization to the coal strata. At length, as the temperature 



