600 



J. CLIFTON WARD ON THE GRANITIC, GRANITOID, AND 



occurrence of Phosphates in the Cambrian Rocks"*, some interesting 

 points as to the connexion of phosphoric acid with volcanic rocks 

 were brought forward and discussed. Is the phosphoric acid found 

 in eruptive rocks derived from sedimentary deposits through which 

 they may have broken ? or are these eruptive rocks themselves the 

 sources of the phosphoric supply to all sedimentary beds ? 



If we glance at the accompanying Table, showing the relative 

 amount of phosphoric acid in some of the volcanic rocks of Cumber- 

 land, we must be struck by the large proportion as compared with 

 that in the associated granite, while the metamorphosed trap (?) 

 rock close to the junction contains the largest amount. 





Phosphoric 

 acid. 



Carbonic acid. 



No. 1. Lava, Iron Crag, near Keswick 

 No. 2. „ Brown Knotts „ ,, 

 No. 3. Felstone-like altered ash, Base 

 Brown 



•115 



•281 



•343 

 •204 

 •439 

 •012 



•089 



1-569 

 1-660 



•660 



trace 



trace 



trace 



trace 



No. 4. Felstone-like altered coarse ash, 

 Slight Side 



No. 5. Probable lava-bed, highly al- 

 tered, close to granite, Lingmell Beck 



No. 6. Granite, (Eskdale) S. of Great 

 How 



No. 7. Felstone (contemporaneous) of 

 Aran Mowddwy 





Side by side I have placed in this Table the percentages of phos- 

 phoric and carbonic acids ; and it is an interesting result to notice 

 that as the one increases the other decreases. Since phosphoric acid 

 is not separated from lime by heat alone, and carbonic acid is readily 

 so separated, have we not, in these inverse proportions, another 

 argument for a great change having been effected among the original 

 constituents of these volcanic rocks by extreme metamorphism ? For 

 it should be observed that the two lava-beds standing first in the list 

 do not occur in the very metamorphosed region ; and of the three 

 following examples, that contains the highest percentage of phosphoric 

 acid which probably represents a highly metamorphosed bed of lava. 



With regard to the high percentage of carbonic acid in Ncs. 1 and 

 2, it may be thought that these beds have been more exposed to 

 infiltration from above than the others ; but I do not think this can 

 possibly be the case, since these lavas are certainly lower down in 

 the series than Nos. 3, 4, and 5, and it seems more reasonable to infer 

 that an equivalent quantity of carbonic acid may have existed in the 

 other examples, but has been driven off by metamorphism, acting 

 more forcibly at one area than another. 



If we compare the felstone-like altered ashes of Cumberland with 

 the undoubted contemporaneous felstone (old lava) of Aran Mowddwy, 

 * Quart. Journ. Geol. Soc. vol. xxxi. p. 368. 



