176 A. Harder — A Cordierite-hearing Lava 



I think, conclude that the earth-shake was due probably to a slip of 

 this fault, but possibly to a subsidence along a band determined by, 

 and closely adjoining, the fault. What the depth of the focus was 

 we have no means of determining exactly, but it can hardly have 

 been greater, and was probably much less, than a quarter of a mile, 

 that is, considerably less than the depth of the present workings^ 

 which are from 800 to 1,100 yards below the surface. 



That the shock was primarily due to work in connection with the 

 mines there can, I think, be little doubt. The slip, whether along 

 the fault or otherwise, can hardly have been precipitated directly by 

 the withdrawal of the coal, but rather, as suggested to me by 

 Mr. Joseph Dickinson, by the pumping of water in the overlying 

 beds.^ On this supposition, the slight depth of the focus, its great 

 horizontal and small vertical dimensions, and the long interval that 

 has elapsed since the working of the coal near the fault, would all 

 receive a satisfactory explanation. 



VI. — A CORDIEKITE-BEARING LaVA FROM THE LaKE DISTRICT. 

 By Alfred Harkek, M.A., F.R.S. 



ALTHOUGH the volcanic rocks of the English Lake District 

 have received notice from time to time, any systematic account 

 of them from the petrographical side has yet to be written. The 

 most recent contribution, by the late Mr. E. E. Walker,- treated 

 especially of the mode of occurrence of the garnet, which is so 

 common a constituent, not only of the lavas and tuffs, but of the 

 associated intrusive rocks, probably referable to the same Ordovician 

 age. There can be no doubt that this mineral is sometimes a primary 

 constituent, but very often a product of metamorphism. The object 

 of the present note is to record the occurrence in one instance 

 of a rarer mineral, which has not hitherto been observed in this 

 series of rocks. Cordierite is found as a product of thermal meta- 

 morphism in the Coniston Flags near the Shap Granite,^ and in the 

 Skiddaw Slates of the Skiddaw granite area.* In the latter it is 

 remarkably abundant and wide-spread.® The mineral is now found 

 to occur, as an exceptional constituent, in the volcanic series. 



The specimen was collected sixteen years ago on Sty Head Pass, 

 just south of the watershed. As it does not, to the eye, present any 

 unusual appearance, its occurrence was not more particularly noted. 

 It comes then in the midst of the volcanic succession, between the 

 principal group of basic lavas and the thick breccias and tuffs which 

 build the central mountains of the district. Dr. Marr " has expressed 

 the opinion that a large part of the garnetiferous rocks which occur 



^ For a similar suggestion see Geol. Mag., Dec. V, Vol. II (1905), p. 223. 

 - Quart. Journ. Geol. Soc, vol. Ix (1904), pp. 70-104. 



3 Hutchings, Geol. Mag., 1894, pp. 65, ti6. 



4 Harker,Und., pp. 169, 170. 



5 Barker, Naturalist, 1906. 



6 Proc. Geol. Assoc, vol. xvi (1900), pp. 476, 477, and map, pi. xiii. 



