Vol.50-] ANNIVERSARY ADDRESS OF THE PRESIDENT. 121 



of the Upper Silurian, whilst the Coniston Limestone completes 

 the sedimentary series. The volcanic rocks in contact belong to the 

 upper part of the ' Borrowdale Series ' and are represented by the 

 rhyolitic and andesitic groups ; the rocks on the north of the granite 

 being subsequently described as basic andesites. 



Thermo-metamorphism in andesitic rocks has hitherto, Messrs. 

 Harker and Marr say, received but little attention, although Prof. Judd 

 has adverted to some changes of this kind in the andesites or 

 ' propylites ' of the "Western Isles of Scotland. The andesitic group 

 is in contact with the Shap granite round one half of its circumference, 

 and the andesitic lavas are stated to afford some of the most instructive 

 examples of thermo-metamorphism in the district, the process of 

 transformation being traceable in all its stages. What those pro- 

 cesses are can be gathered only from a careful perusal of the paper 

 itself. The production of biotite, hornblende, and augite is narrated 

 with especial precision, and in addition to these the following 

 minerals of metamorphic origin are quoted from the andesites and 

 andesitic ashes, viz. quartz, orthoclase, several kinds of plagioclase, 

 colourless mica (muscovite), sphene, apatite, magnetite, and pyrites. 



The metamorphism of the rhyolitic rocks, of the Coniston Lime- 

 tone series, and of the Silurian rocks is very fully treated ; but it 

 will be sufficient on the present occasion to notice one or two points 

 only with reference to the metamorphism of the Shap Fell rocks 

 generally. Thus, in estimating facilities for contact-metamorphism 

 in different rocks, it is observed that the substances resulting from 

 the ' weathering ' of the rocks were more susceptible to change 

 than minerals of direct igneous origin, and, as may be readily 

 supposed, the original quartz-sand in the flags proved especially re- 

 fractory. The several minerals detected in the various metamor- 

 phosed rocks, as products of the metamorphism, are summarized in a 

 table. The absence or rarity of some characteristic ' contact- 

 minerals ' of other districts is rather striking. Some of these, they 

 say, are products which probably require special ' mineralizing 

 agents,' such as the compounds containing fluorine ; but the almost 

 complete absence of andalusite (chiastolite), staurolite, and garnets 

 (other than lime-garnets in connexion with the Coniston Limestone) 

 is certainly remarkable. This view of the case is somewhat modified 

 in the list of metamorphic minerals appended to their second paper ; 

 since andalusite, cyanite, and sillimanite are all quoted from the 

 metamorphosed acid lavas and ashes, though possibly these are ex- 

 ceptional instances which serve to prove the general rule. 



In their Supplementary Notes on the metamorphic rocks round 



