22 



ME. H. C. SAECiEXT OX LOWEE CABBOXIFEEOUS [vol. Ixxiu, 



SiOo 



49-24 



Feb 



MnO 



MgO , 



CaO i 



Na.O I 



KoO 



TiOo I 



CO2 ' 



H20(liygi-osc.) 



HoOCcomb.)... 



Other con- ) 



stituents S 



6-09 

 7-18 

 0-29 

 3-02 

 5-26 

 5-21 

 2-10 

 1-84 



l-'08 

 1-61 



1-77 



II. 



47-56 40-55 43-13 



AM);, ' 15-84 14-27 



1-63 

 6-80 

 0-30 

 4-90 

 10-96 

 4-61 

 0-27 

 2-40 

 2-95 

 0-42 

 2-65 



0-54 



III. 



113 

 9-46 

 0-20 

 5-20 

 6-06 

 4-76 

 0-27 

 2-95 

 7-85 

 0-27 

 3-89 



0-90 



IV. 



16-65 23-25 



1-87 

 4-81 

 trace 

 6-50 

 5-58 

 3-60 

 3-04 

 not est. 

 3-50 

 1-06 

 3-76 



47-03 

 22-45 



7-00 



8-79 

 2-92 

 2-63 

 4-55 

 not est. 

 1-90 



3-65 



VI. 



VII. 



0-82 

 6-59 



1-2 

 5-5 



Total 



100-53 100-25 , 100-14 ino-]0 | 10092 



L 



I. Mugearite, Druim na Criche, Skj'e (W. Pollard). 'The Tertiary Igneous 

 Rocks of Skje ' Mem. Geol. Surv. Scotland, 1904, p. 263. 

 Spilite, Tregedden, South Cornwall (E. G. Kadley). Quoted from H. Dewey 

 & J. S. Flett, 'On some British Pillow-Lavas & the Rocks associated 

 with them ' Geol. Mag. dec. 5, vol. viii (1911) p. 206. 

 Spilite, Devonport Workhouse Qnarrv' (W. Pollard). ' The Geology of the- 

 Country around Plymouth & Liskeard ' Mem. Geol. Surv. 1907, p. 97. 

 IV. Spilitic lava, Tideswell Dale (E. Siukinson). 



V. Spilitic lava, Knot Low, Millers Dale {E. Siukinson). 

 VI. Spihtic lava, Masson, Matlock. Partial analysis (E. Siukinson). 



IL 



III 



VII. Spilitic lava, Masson, Matlock. Partial analysis (C. S. Garnett), 



YI. The Tuffs. 



Although the scope of this paj^er is Hmited to tlie lava-flows, it 

 is interesting to note that the tuffs, under the microscope, are not 

 infrequently seen to contain felspar-crystals with straight extinc- 

 tion. Dr. Bemrose^ records the occurrence of such felspars at the 

 following tuff outcrops : Cressbrook Dale. Monk's Dale, Cracken- 

 dale, Ember Lane, Grange Mill, Woodeaves Vent. He also note& 

 the presence in specimens fi'om Grrange Mill of 



' a felspar-like material here and there in the lapilli which is biaxial, and may 

 be secondary albite.' - 



AYater-clear, untwinned felspars also occur in some of these tuffs. 

 On the assumjition that, Avhen explosive action occurs, it takes ])lace 

 at the commencement of the volcanic episode, we have thus fm'ther 

 evidence that the alkalies were to some extent concentrated in the 

 upper part of the magma. 



^ Q. J. G. S. -vol. 1 (1894) pp. 629-38. 

 ^ Ibid. p. 635. 



