156 LYELL'S ELEMENTS OF GEOLOGY. 



Simultaneous Origin of the four Classes of Rocks. 



this state of things some of the residuary mineral ingredients of 

 the primeval ocean were precipitated, and formed deposits (the 

 transition strata of Werner), half chemical and half mechanical, 

 and containing a few fossils. 



By this new theory, which was in part a revival of the doc- 

 trine of Leibnitz, published in 1680, on the igneous origin of the 

 planet, the old ideas respecting the priority of all crystalline rocks 

 to the creation of organic beings, were still preserved ; and the 

 notion, that all the semi-crystalline and partially fossiliferous 

 rocks belonged to one period, while all the earthy and uncrys- 

 talline formations originated at a subsequent epoch, was also 

 perpetuated. 



It may or may not be true, as the great Leibnitz imagined, 

 that the whole planet was once in a state of liquefaction by heat ; 

 but there are certainly no geological proofs that the granite which 

 constitutes the foundation of so much of the earth's crust was 

 ever in a state of universal fusion. On the contrary, all our 

 evidence tends to show that the formation of granite, like the 

 deposition of the stratified rocks, has been successive, and that 

 different portions of granite have been in a melted state at dis- 

 tinct and often distant periods. One mass was solid, and had 

 been fractured, before another body of granitic matter was in- 

 jected into it, or through it, in the form of veins. In short, the 

 universal fluidity of the crystalline foundations of the earth's 

 crust, can only be understood in the same sense as the univer- 

 sality of the ancient ocean. All the land has been under water, 

 but not all at one time ; so all the subterranean unstratified rocks 

 to which man can obtain access have been melted, but not simul- 

 taneously. 



In the present work the four great classes of rocks, the aqueous, 

 plutonic, volcanic, and metamorphic, will form four parallel, or 

 nearly parallel, columns in one chronological table. They will be 

 considered as four sets of monuments relating to four contem- 

 poraneous, or nearly contemporaneous, series of events. I have 

 endeavoured, in the Frontispiece, to express the manner in which 

 members of each of the four classes may have originated simul- 

 taneously at every geological period. According to this view, the 

 earth's crust may have been continually remodelled, above and 

 below, by aqueous and igneous causes, from times indefinitely re- 

 mote. In the same manner as aqueous and fossiliferous strata 

 are now formed in certain seas or lakes, while in other places 

 volcanic rocks break out a,t the surface, and are connected with 

 reservoirs of melted matter at vast depths in the bowels of the 

 earth, so, at every era of the past, fossiliferous deposits and 

 superficial igneous rocks were in progress contemporaneously 



