H. Keeping — The Age of the CreecJihnrrow Limestone. 555 



Geological Society of Dublin, 1861, vol. ix, p. 288) he describes as 

 "occurring in actual contact with garnet limestones wherever we 

 find these rocks ". This Sphene-rock consists of allotriomorphic and 

 hypidiomorphic felspars, with quartz, idiomorphicdiopside and sphene, 

 and in some localities zoisite, scapolite, etc. 



It is my experience that the Sphene-rock always occurs in the 

 limestone, and never represents the mixed rock at the margin of the 

 limestone xenoliths. It generally takes the form of regular and 

 definite granite veins intrusive in the metamorphosed limestone, the 

 veins having absorbed material from that rock by their intrusion to 

 considerably modify their original nature. The formation of this 

 Sphene-rock is interesting, and has been studied by me in considerable 

 detail. In practically every instance where the metamorphosed lime- 

 stones contain granite veins the latter are of the nature of Sphene- 

 rock, and this rock was not found to occur under any other conditions. 



In a few localities the enveloping granite for an inch or so at the 

 contact with the limestone contains sphene and a trace of pyroxene. 

 At Annagary, a few feet of pyroxenic granulitic rock, also containing 

 sphene, is developed at the junction of the limestone xenoliths with 

 the enclosing granite. 



It is my intention in the near future to describe at length elsewhere 

 the Sphene-rock and its mode of occurrence, as well as the various 

 types of metamorphosed limestone, which, for the sake of convenience 

 in describing, I have arranged under several headings indicated by 

 their mineralogical constitution, namely — 



Garnet-calcite-pyroxene rock, 



Garnet- Wollastonite rock, 



Idocrase-calcite rock, 



Epidote-actinolite-quartz rock, 



Scapolite rock, 



Actinolite-calcite rock, 

 as well as calc-silicate hornfels, pyroxene granulites, etc. 



The chief localities examined were the following : Barnes Gap, 

 Glen, Sessiagh Bay, Bunbeg, Annagary, Loughanure, Lough Atirrive, 

 Poisoned Glen, Ardmeen, near Anure Lough, Dunlewy, Doochary 

 Bridge, Glenleghan, Lough Xambraddan, Fintown, and Toberkeen. 



The minerals noted in the calc-silicate limestones in addition to 

 calcite are : Garnet, idocrase, pyroxenes, Wollastonite, tremolite, 

 actinolite, pistacite, quartz, scapolite, zoisite, apatite, fluorite, and 

 mica. Some of these minerals are particularly well formed, and have 

 found place in most of the chief museums of Great Britain and 

 Ireland. 



IX. — Sedgwick Museum Notes. 

 On the Age oe the Creechbakeow Limestone. 

 By Henry Keeping. 



ON the north side of the outcrop of the Chalk in the Isle o 

 Purbeck, there is an outlier of Tertiary beds the exact age of 

 which has given rise to some discussion. There must be some 



