28 Anniversary Address of the 



In the first volume of the " Memoirs of the Survey of 

 Great Britain," Professor Ramsay has shewn that the miss- 

 ing beds, removed from the summit of the Mendips, must 

 have been nearly a mile in thickness, and he has pointed out 

 considerable areas in South Wales and some of the adjacent 

 counties of England, where a series of palaeozoic strata not 

 less than 11,000 feet in thickness have been stripped off. 

 All these materials have of course been transported to new 

 regions ; and when it is shewn by observations in the same 

 " Survey" that the palaeozoic strata are from 20,000 to 

 30,000 feet thick, we have a counterpart of older date of 

 denuding operations on a scale of similar grandeur, for what 

 has been carried away or borrowed from one space must 

 always have been given to another. The gain must always 

 have equalled the loss, and sediment deposited in one area 

 must be the measure of the quantity of pre-existing rock 

 cleared away elsewhere. The announcement of this principle 

 may seem, perhaps, like insisting on a truism, but I find it 

 necessary, because in many geological speculations I observe 

 it is taken for granted that the external crust of the earth 

 has been always growing thicker, in consequence of the 

 accumulation of stratified rocks, as if they (and possibly the 

 contemporaneous rocks of fusion, in progress far below) 

 were not produced at the expense of pre-existing rocks, 

 stratified and unstratified. Whether indeed the trap and 

 granite of successive ages were formed by the melting of 

 matter previously solidified, will be questioned by those who 

 contend that the globe was originally a fused mass, and who 

 also assume (still more gratuitously as appears to me), that 

 geological monuments have reference to the period when the 

 melted nucleus was passing to a more and more solid state. 

 But even those geologists must admit that strata of the old 

 red sandstone, or of any other ancient or modern rock of 

 mechanical origin, imply the transportation from some other 

 region, whether contiguous or remote, of an equal amount of 

 solid material, so that the stony exterior of the planet has 

 always gi*own thinner in one place whenever by accessions 

 of new strata it has acquired density in another. The vacant 

 space left by the missing rocks, after extensive denudation, 



