68 



LIMESTONES. 



' 



gSSt N0S ' 2 ° and 22 ' and in vertical section No. 22 of the « Geo 

 — logical Survey." — A. C. R. 



Wall-case 42. 



Wall-case 4 



The higher shelves of this case contain limestones, ar- 

 ranged not stratigraphically, but, as far as the sizes of the 

 specimens allow, generally with reference to their qualities. 

 The highest shelf contains large specimens of various kinds. 

 The second and part of the third shelves are devoted to 

 the more solid and compact limestones, which, in Britain, 

 chiefly lie in the older or palaeozoic strata. This peculiarity 

 is, perhaps, partly the effect of mere age, partly of the 

 repeated disturbance and great pressure to which many of 

 the older rocks of the British area have been subjected. 

 Shelves 3, 4, and 5, from No. 40 onwards, partly contain 

 Secondary and Tertiary limestones, chiefly liassic, oolitic, 

 cretaceous, and Eocene or lower tertiary. The Lias, and some 

 of the shelly oolitic limestones, are comparatively hard, but as 

 a rule, the latter are softer than the more ancient limestones. 

 Many of the Oolites form ordinary building stones, and the 

 Chalk is the softest of limestones. This may be due in part to 

 the circumstance that in general in England, the secondary 

 rocks lie almost horizontally. They have been little dis- 

 turbed, and no intense pressure has been applied to them com- 

 parable to that which has affected the old contorted strata. 

 In the Alps, however, and other mountain regions, limestone 

 strata of Secondary and Tertiary ages are as much indurated 

 as our oldest limestones. 



the limestones not marked freshivater are 

 The Carboniferous limestone lies beneath 

 the Coal measures, and in South Wales, Somersetshire, &c, 

 attains^ a thickness of 2,300 feet. The Lias limestones 

 occur in bands, and are interstratified with beds of clay. 

 The Oolite limestones are often shelly, and oolitic, or com- 

 posed of small rounded concretionary grains cemented 



of marine origin. 



characters are 



The 





I 





o 



i 



a 



€ 



5l 



V 



This 

 inner' 



i 



i irlii 

 fcira 



tk ton 

 in the 

 Parbec 



riin 



r 



\\ 



are hot 



e 



Hi 



. 1 » 



« 



S 



