1867.] 



TIMINS MALVEEN HILLS. 



355 



The atomic proportion of the silica to the bases was also found to 

 be nearly the same in the rocks containing the carbonates as in 

 other rocks in the vicinity from which they were absent. It would 

 therefore appear that the presence of the carbonate of lime cannot 

 there be altogether the result of decomposition or infiltration. Dr. 

 Holl has observed that these calcareous rocks do not represent the 

 mass, but occur as beds, usually at the top or bottom of the lava 

 beds. They would therefore have been formed at the commence- 

 ment, or at the close, of the period of volcanic activity, when its force 

 was least energetic, and the temperature probably lowest. Now the 

 thermal waters of spent volcanoes are often found to be charged with 

 carbonate of lime. The observations of Scacchi on the emanation- 

 products of Vesuvius have also shown that eruptions of lava are ac- 

 companied by other substances than its ordinary constituents. Car- 

 bonate of hme, as is well known, retains its carbonic acid, even with 

 access of atmospheric air, at a dull-red heat, and at a far higher tem- 

 perature when fased with the carbonate or sulphate of soda, or with 

 chloride of calcium. The emanation of carbonate of lime with vol- 

 canic matter towards the close of an eruption is therefore probable ; 

 and as the lava-flows in the black shales proceeded from numerous 

 outbursts of limited extent and duration, the intimate dissemination 

 of carbonate of lime in some portions of the rock at the period of its 

 eruption may thus be accounted for. 



Of the thin beds interstratified with the shales, one only, IX., has 

 the composition of volcanic ash. The others, X., XIII., have that of 

 the shales with which they are associated, with the occasional addi- 

 tion of carbonates, XI., XII. These, together with the associated 

 beds of shale, were probably derived from the decomposition of lavas 

 of the Black-shale period. 



II. Eruptive Rocks of the HoUyhush Sandstone. Holl, Z. c. pp. 87, 

 88. PhiUips, I. c. 52, 53. 

 The appearance of many of these rocks is such as to justify the 

 term " felspathic traps " by which Professor Phillips has designated 

 them. But in those which I have examined I have never found the 

 atomic proportion of the silica to the bases to exceed 2:1. 





















'T5 









t)H 



«f-. 







i 



1— 1 . 









13 



o 



^2 



si 



o g 



i 



1^ 



o ^ 



11 





w 



< 



Oh^ 



OQ 



C^ 



'^ 



^ 



^ 



< 



XVI. 



58-07 



19-14 



5-90 





0-25 



1-95 



1-00 



1-96 



11-73 



XYII. 



54-01 



17-45 



8-05 







2-36 



3-53 



2-95 



11-65 



XVIII. 



57-64 



17-34 



7-71 



6-20 



0-15 



2-42 



060 



3-60 



10-34 



XIX. 



52-12 



18-48 



8-91 



0-25 



0-20 



2-52 



6-24 



4-50 



6-78 



XX. 



66-03 



18-51 



6-14 



0-40 





2-39 



2-69 



2-45 



11-39 



XVI. Light-coloured felspathic rock, west of Bagged Stone Hill. 



XVII. From the same place, of a darker colour. 



XVIII. Similar rock, of a light colour, from the north side of a small 

 quarry, near an oak tree, S.S.E. of Fowlett's Farm ; decomposed. 



