OLDER AND YOUNGER FORMATIONS. 85 



different aspect, and require all the ingenuity of science to 

 interpret their history. 



This relative antiquity of rock-deposits may be still more 

 clearly shown by the formations of our own islands. The 

 carse-lands of the Tay and Forth and the fens of Lincoln- 

 shire are recent alluvia, and younger than the blue clays 

 and gravels over which they are spread ; the stratified sands 

 and clays and gravels in the neighbourhood of London are 

 younger than the chalk and greensands that lie beneath ; 

 and these chalk-hills and greensands of Kent and Surrey 

 are newer than the calcareous sandstones and limestones of 

 Portland on which they repose. Again, the oolites or roe- 

 stones of Portland are younger than the underlying red 

 sandstones and marls of Cheshire, and these newer than 

 the coals and ironstones of Lancashire that are spread out 

 beneath. The coals of Lancashire, Northumberland, and 

 Fife are not so old as the underlying red sandstones and 

 flagstones of Forfarshire; and these again are much 

 younger than the still deeper slates and crystalline schists 

 of the Scottish Highlands. NOT is it superposition alone 

 that proves this relative antiquity. Mineral structure and 

 texture become more intensified with age j fossil organisms 

 become more obscure, and the further we descend in time 

 the wider the divergence from the genera and species that 

 now people the globe. Everything in the earth's crust 

 speaks to this relative antiquity to this old, older, oldest ; 

 and it is the object of the present Sketch to describe the 

 earlier of these formations, and to depict, as far as Geology 

 can, the aspects of the periods when they were gradually 

 accumulating in the primeval waters. 



Before entering on this description, however, it may 

 render matters more intelligible to state, and what indeed 

 has been already detailed in No. 1 of these Sketches, that 



