GEOGRAPHICAL EVOLUTION 847 



tion of these meteorites, may remain in appreciable quan- 

 tity. In this case, again, it is not needful to suppose that 

 meteorites have disappeared over these ocean depths more 

 numerously than over other parts of the earth's surface. 

 The iron granules have no doubt been as plentifully showered 

 down elsewhere, though they cannot be so readily detected in 

 accumulating sediment. I know no recent observation in 

 physical geography more calculated to impress deeply the 

 imagination than the testimony of this presumably meteoric 

 iron from the most distant abysses of the ocean. To be 

 told that mud gathers on the floor of these abysses at an 

 extremely slow rate conveys but a vague notion of the tardi- 

 ness of the process. But to learn that it gathers so slowly, 

 that the very star-dust which falls from outer space forms 

 an appreciable part of it, brings home to us, as hardly any- 

 thing else could do, the idea of undisturbed and excessively 

 slow accumulation. 



From all this evidence we may legitimately conclude 

 that the present land of the globe, though formed in great 

 measure of marine formations, has never lain under the 

 deep sea; but that its site must always have been near 

 land. Even its thick marine limestones are the deposits 

 of comparatively shallow water. Whether or not any trace 

 of aboriginal land may now be discoverable, the characters of 

 the most unequivocally marine formations bear emphatic 

 testimony to this proximity of a terrestrial surface. The 

 present continental ridges have probably always existed in 

 some form, and as a corollary we may infer that the pres- 

 ent deep ocean basins likewise date from the remotest 

 geological antiquity. 



2. Crystalline. While the greater part of the frame- 

 work of the land has been slowly built up of sedimentary 

 materials, it is abundantly varied by the occurrence of 

 crystalline masses, many of which have been injected in 

 a molten condition into rents underground, or have been 

 poured out in lava-streams at the surface. 



Without entering at all into geological detail, it will be 

 enough for the present purpose to recognise the characters 

 and origin of two great types of crystalline material which 

 have been called respectively the Eruptive and Metamorphic. 



