296 PROF. A. H. COX AND ME. A. K. WELLS ON THE [vol. lxxvi, 



samples water-clear, excej)t for fairly numerous primary inclusions 

 of apatite, chlorite (after hornblende), and sphene. 



The dark minerals, hornblende and magnetite, need but little 

 mention ; the distinctive feature is their great abundance, as the} r 

 make up nearly a third of the bulk of the rock. The horn- 

 blende is mainly pale actinolite of rather acicular habit, and is 

 crowded with magnetite-grains. The acicular character of the 

 dark minerals in marginal modifications of granophyres has been 

 noted by Dr. A. Harker 1 and by Mr. 11. H. Kastall 3 in the 

 Carroek-Fell and Buttermere intrusions respectively. 



This type (2) may be followed right up to the margin of the 

 country-rock, whatever that may be — diabase, rhyolitie ash, etc. 

 Along the actual margins the marginal basic rocks are distinctly 

 chilled over a thickness of 3 to 10 feet. The chilled rocks [type 1, 

 C 209 & C 304] resemble those described in the preceding para- 

 graph, but are naturally of finer grain ; and those felspars that 

 were idiomorphic tend to lose their idiomorphism, partly owing to 

 the way in which they interlock irregularty one with the other, and 

 partly owing to the distribution of the abundant dark minerals. 

 In the case of plagioclase, however, indications of the characteristic 

 shape may still be seen, whereas the orthoclase is entirely allotrio- 

 morphic. 



.Returning to the unchilled basic rocks and following them 

 towards the granophyre, we notice various changes. The plagio- 

 clase becomes more idiomorphic away from the chilled zone, and 

 at the same time it builds larger crystals than in the normal 

 granophyre. Quartz soon makes its appearance, first as tiny inter- 

 stitial patches, then as distinct blebs [C 216]. The appearance 

 of the blebs is then followed by the incoming of first small, and 

 then larger, amounts of extremely fine-grained micixmegmatite 

 [type 3, C 217] which gradually increases in coarseness as the 

 rocks become more acid. In these slightly less basic rocks an 

 intensely-pleochroic hornblende (yellow to deep blue-green) takes 

 the place of the pale actinolitic variety found in the most basic of 

 the marginal rocks. Simultaneously with the incoming of quartz 

 and its gradual increase, an intensely-pleochroic biotite also appears 

 in criss-cross wisps which increase in amount at the expense of 

 hornblende. These somewhat less basic marginal rocks also contain 

 allanite, as in the normal granophyre [C 220, fig. 6, p. 293 & 

 PI. XIX, fig. 2]. 



As the result of movement during consolidation a certain 

 amount of admixture of previously- differentiated materials has 

 taken placQ. Thus the most basic type (2) may contain xenoliths 

 of chilled material, type 1 (see PI. XIX, fig. 4), while the more acid 

 and granophyric type (3) contains xenoliths of both the preceding 

 types (1 & 2). In such cases, acidic and basic matei'ials were 

 brought into unnatural juxtaposition, resulting in the partial or 



1 Q. J. G. S. vol. li (1895) p. 127. 



2 Ibid. vol. lxii (1906) p. 265. 



