102 Geological Changes from Alterations of the 



particularly when we take into considei'ation the small depth to which 

 they would probably descend in the earth's crust. 



We have also to regard the effects arising from the dislocation of 

 the strata, as noticed by Sir John Lubbock. There are few geolo- 

 gists who are not now prepared to admit that the surface of the 

 earth, since we may assume any solidity in that surface, has bef n in 

 an unquiet state, some large areas moving upwards, some downwards, 

 and these movements sometimes repeated in the same area ; deposits 

 crushed and folded against each other here and there in long lines, 

 so that parts of them are thrust high up above the levtl of the sea, 

 while masses of accumulations are forced asunder in other situations, 

 and mineral matter raised from beneath occupies parts of the area 

 over which they previously spread. Up to the present time mineral 

 matter is here and there vomited forth in fusion, or blown out of 

 vents by the discharge of vapours and gases, and large tracts of 

 the solid surface of the earth are violently shaken, and portions of 

 land raised or depressed. We also know that at the present, slow 

 changes in the relative levels of sea and laud are being eflected. 

 Thus from our own expei'ience and from the study of what has 

 formerly happened, we find that the surface of our planet is and has 

 been, during the lapse of such geological time as we can trace, in an 

 unquiet state. We of course know nothing of the lieight to which 

 the crushing or elevating of rocks into mountain-chains may have 

 forced mineral accumulations, though we may often infer that very 

 great heights are but the remains of rocks, the removed portion of 

 which rose still further into the atmosphere ; but, taking the Hima- 

 layan chain as the highest land, we liave nothing rising six miles 

 above the sea-level. If we iricrease this height to ten miles, we should 

 still have an insignificant fraction of the earth's radius. 



The researches of Mr Hopkins lead him to infer that at present 

 the solid crust of the earth cannot be less than 800 to 1000 miles 

 thick. Supposing this to be so, the hypothesis of a cooling globe 

 would give a less thickness in past geological times, one gradually 

 diminishing to the early period when solid matter could be first 

 formed. 1 need scarcely call your attention to the view which has 

 been taking of the forcing-up of mountain-chains, and the unequal 

 tilting and adjustment of masses of the surface to accommodate the 

 Crust to the still fluid mass beneath, as cooling proceeded. Neither 

 need I speak of the effects which would follow from the action of the 

 heated and still fluid mass upon the poilions of the fragments which 

 may have descended different depths into its surface, or of the intru- 

 sion of the molten matter amid the broken masses ; we have only to 

 inquire how far these breakings-up and squeezings of the previously 

 solid crust at different times is likely to have interfei-ed materially 

 with its general uniformity, so that any important change in the 

 earth's axis, with its geological consequences, may have resulted. 



As regards the mineral matter thrust up into the atmosphere, we 



