as exhibited in the Devonian Limestones of Devonshire. 25 



Stonehouse No. 3. (Chemical analysis.) 



Inorganic clay 222 



Carbonate of lime 4-2*2~| ,. 



Carbonate of magrnesia 32""' 



.f, I dolomite. 



Carbonateof protoxide of iron (oxidized) 3 

 Peroxidized pyrites '3 



lOO-O 

 (Physical analysis.) 



More or less detached rhombic crystals 1 „ i .o 



(•001 to "OOo inch in diameter) . J 

 Indistinct crystals, &c. surrounding the 1 fio.a 



above J 



Detached red crystals of peroxidized^ .„ 



pyrites J 



100-0 



Near Ilfracombe occurs a limestone foliated with dolomitic 

 crystals in a peculiar manner, as will be described further on ; 

 some parts being not yet oxidized, but others converted into 

 yellow folia by the oxidation of the protoxides of iron and 

 manganese. 



Ilfracombe No. 8. (Chemical analysis.) 



Inorganic clay 2'6 



Carbonate of Hme 14*51 25*4 



Carbonate of magnesia 6" 8 I dolomite 



Carbonate of protoxide of iron (oxidized) 3'4 f of equal 

 Carbonateofprotoxideof manganese (oxidized) 'TJ equivalents. 

 Excess of carbonate of lime . . . . 72 '0 



100-0 



(Physical analysis of two portions.) 



Rhombic crystals in bands and layers 34-5 50*8 



Joints of encrinites 0-0 -8 



Organic clay 65-5 48-4 



100-0 100-0 

 In this the amount of crystals of dolomite or brown-spar so 

 much exceeds what would occur if the carbonates of magnesia, 

 iron, and manganese were combined with equal equivalents of 

 that of lime, that I conclude that the crystals must either be 

 more highly calcareous, or part of them pure calcareous spar. 

 This is certainly the case in a limestone from near Plymouth 

 {Eburton, Plymouth No. 1), consisting of alternate folia of un- 

 altered organic clay and dark-coloured material, which, when 

 examined by the microscope, is seen to be composed of rhombic 



