310 



G. W. Tyrrell— Tertiary Dykes 

 Table II. 



1. Cumbraite, Tertiary N.W. dyke (interior glassy facies), II, 4. 3. 4. (tonalose), 

 s Eerie Port, Great Cumbrae, Firth of Clyde. Anal, by Chetai Yu, B.Sc. ; 



alkalies, Ti0 2 and P 2 5 , by A. Scott, M.A., D.Sc. 



2. "Pitcbstone" (Cumbraite, Eskdale type), N.N.W. dyke with " sheath-and 



core " structure, II', 4'. 3. 4. {tonalose), Eskdale, Dumfriesshire. Quoted 

 from Sir A. Geikie, 1880, p. 253. 



3. Leidleite (glassy part of sill showing "sheath-and-core" structure), II, 4.3.4. 



(tonalose), 2 miles S.S.W. of Pennyghael, Mull. Anal. E. G. Badley, 

 Summ. Prog. Geol. Surv. for 1912 (1913), p. 69. 



4. Inninmorite (inclined sheet, "contains small phenocrysts of basic plagio- 



clase, and has acicular augite in the glassy base"), 'H, 4. 2 (3). 4. 

 (tonalose-dacose) ,1 mile S.S.W. of Pennyghael, Mull. Anal. E. G. Badley, 

 Summ. Prog. Geol. Surv. for 1912 (1913), p. 69. For other analyses of 

 leidleite and inninmorite see E. M. Anderson and E. G. Badley (1916, 

 p. 212). 



5. Average Andesite (Daly), 'II, 4. 3. 4. (tonalose). B. A.Daly, Igneous Bocks 



and their Origin, 1914, p. 26. 



6. Average hypersthene-andesite, II, 4. 3'. 4. (tonalose). Calculated from 



71 analyses of rocks described as hypersthene-andesite, hypersthene- 

 augite-andesite, bronzite- and enstatite-porphyrite, enstatite-diabase- 

 porphyry, and bronzite-tholeiite ; taken from Iddings, Igneous Bocks, 

 vol. ii, 1913 ; Iddings & Morley, paper on " Japanese Volcanic Bocks ", 

 Proc. Nat. Acad. ScL, Washington, vol. ii, 1916 ; Bosenbusch, 

 Oesteinslehre, 3rd ed., 1910; Washington, Prof. Paper 14, U.S. Geol. 

 Surv., 1903, etc. 



Comparing the Cumbrae types with the related leidleite and 

 inninmorite of Mull, it may be noted first that the latter are richer 

 in combined water, and therefore in glass, than the Cumbrae types. 

 Leidleite differs otherwise in containing a smaller percentage of 

 lime, due probably to the absence of anortbite. This results in an 

 almost exact reversal of the proportions of diopside and hypersthene 

 in the norms of the two rocks (Table III, 1, 3), but otherwise the 



