Mr Poulett Scrope's Considerations on Volcanos. 361 



of the ocean and atmosphere diminished further, the quantity of water 

 taken into circulation decreased ; the continents were no longer deluded 

 by perpetual floods of rain, and organized nature took possession of them 

 also ; the marine deposits contained less of precipitated matter, and be- 

 came more earthy, and less crystalline ; strata of shales, dull limestones 

 chalk, marl, sands, and clay, succeeded those of clay-slate, marbles, and 

 sandstones, until the gradual change wrought by the slow refrigeration of 

 the outer zones of the globe brought about the condition in which it ex- 

 sists at present. 



The author remarks that, from the circumstances of their origin, the 

 rock formations of every Kind or age must have been more or less strictly 

 local; and that, though the formations of any particular epoch will un- 

 questionably have some points of general resemblance all over the globe, 

 it would be absurd to suppose the same series of beds to have been depo- 

 sited contemporaneously over the whole of its surface. 



The author sums up, by attributing the production of the mineral mas- 

 ses, as at present observable on the surface of our planet, to three sources, 

 distinct in their nature, but of which the products have been often con- 

 fused and mingled together from circumstances of isochronism or collocation. 

 These are, 1. The precipitation of some minerals, particularly silex and 

 carbonate of lime, from a state of solution in water, as its temperature was 

 diminished, &c. 



2. The subsidence of suspended or fragmentary matter from water; to- 

 gether with the accumulation and decomposition of the shells of molluscs, 

 corals, &c. 



3. The elevation of crystalline matter through fissures in the crust of 

 the globe. 



The author conceives, that all the characteristic differences observable 

 in the successive formations of every kind, may be satisfactorily traced to 

 the gradual diminution in frequency and energy of those productive causes, 

 the varying nature of the original materials acted on, and the chemical 

 and mechanical changes they have undergone during the process ; and with 

 due allowance for these circumstances, these three modes of production 

 are perhaps fully equal to account for the origin of all the mineral masses 

 of the earth's surface. They have also one immense advantage over other 

 hypotheses, and which speaks volumes in their favour, and " this is, thai 

 (hey are all still in operation," and producing results completely analogous 

 to those which arc here attributed to them. In fact, (the author says,) 

 the theory of the globe, which I have thus hazarded, consists simply in 

 the application of those modes of operation which nature still employs, on 

 u large scale, in the production of fresh mineral masses on the surface of 

 the earth, to explain the origin of those which we find there already. 



If, after fair discussion, and with all reasonable allowances, it is found 

 adequate to this purpose, its truth will be established on the soundest 

 possible basis — the same upon which rests the whole fabric of our know- 

 ledge on every subject whatsoever, the supposition, namely, that the law: 



