870 Mr. D. Forbes on the Chemical Composition of 



The analysis will therefore stand as follows : — 



Carbonate of lime 89'34 



Carbonate of magnesia. . . . 0*19 



Carbonate of manganese ... 0'19 



Alumina (trace of iron) . . . 0'07 



Phosphoric acid 0"21 



Organic matter 0*77 



Insoluble 8'29 



Water 0-22 



99-18 

 For the sake of comparison it may now be of interest to tabu- 

 late the whole of the results of the preceding analyses. 



Carbonate of lirae 



Carbonate of magnesia 

 Carbonate of manganese... 

 Alumina and sesquioxide ] 



of iron J 



Phosphoric acid 



Insoluble 



Organic matter ., 



M^ater 



Loss in analysis 



Upper 

 Silurian. 



Dudley. 



9009 

 1-26 



2-30 



0-46 

 5-13 



0-76 



Lower Silurian. 



Ysputty Khiwlas. ,'?'°Sr7' 

 Evan. Llandeilo. 



39-54 

 1-85 



4-68 



016 

 52-27 

 0-73 

 0-53 

 0-24 



19-51 

 1-04 



1-21 



014 



73-13 



3-50 



ll-47 



79-97 

 0-52 



0-82 



056 

 17-85 

 0-56 



100-00 100-00 10000 100-28 100-27 lOO'OO 100-00 



Long- Inve- Kra- 

 mynd. rary. geroe. 



63-10 

 0-SO 



8-51 



0-55 



26-98 



0-33 



73-34 

 0-28 



116 



0-44 



2403 



0-21 



0-54 



89-24 

 0-19 

 0-19 



007 



021 



8-29 

 0-77 



ro-22 



l0-82 



In comparing the above limestones, in respect to tbeir che- 

 mical composition, with those of the later foi'mations, there seems 

 to be but little difference, if we except that the older limestones 

 are generally more impure and, considered as rock masses, seldom 

 contain so large an amount of carbonate of lime as the limestones 

 of the later formations. 



With regard to their respective amounts of phosphoric acid, 

 the now fossiliferous limestones from Church Stretton and Inve- 

 rary, as well as the Llandeilo limestone, contain fully as much 

 phosphoric acid as the subsequent limestones ; and if we take 

 into consideration the respective amounts of carbonate of lime, 

 the same may be said of the Bala limestones. 



That the phosphoric acid present in these limestones has been 

 derived from organic remains seems the more probable, from our 

 not finding phosphoric acid in those varieties of carbonate of lime 

 crystallized from solution ; and amongst all the numerous ana- 

 lyses of calc-spar published, I do not find phosphoric acid men- 

 tioned as occurring; in order, however, to satisfy myself that 



