:288 prof. a. ir. cox and me. a. k. wells on the [vol. lxxvi, 



part the invaded basic material was still too hot to have exerted 

 any chilling effect upon the invading granophyre. 



Since these marginal basic modifications of the granophyre are 

 ■often found in contact with diabases (see p. 282), it might be 

 thought that they represent hybrids formed owing to the ab- 

 sorption of diabase by granophyre, such as have been recorded by 

 observers in other districts. The presence of the basic modification 

 -at localities removed from any actual diabase-intrusion would then 

 be easily explicable either on the theory (i), that the original 

 ^diabase had been modified in its entirety, or (ii), that the hybrid 

 material, originally formed at some diabase-contact, had been subse- 

 quently swept along by the westward movement of the acid magma. 

 This was our own impression when these rocks were first observed. 

 A closer inspection both of the field-junctions and of thin sections 

 -showed, however, that this hypothesis could not hold. The 

 junctions of the basic material with the diabases are alwaj's quite 

 -sharp. This can, as a rule, be readily recognized, owing to the 

 marked differences in texture between the true diabases and the 

 imarginal basic rocks. Moreover, the marginal rocks are sometimes 

 -seen to be distinctly chilled against the normal diabase. Further, 

 there is never any sign of brecciation (intrusion-brecciation) of the 

 ■coarse diabases hy the granophyric magma. Thus the origin of 

 the marginal rocks cannot be connected with the diabase intrusions 

 of the district. 



It is noteworthy that the most basic of these marginal rocks 

 resulting from differentiation in place closely resemble the basic 

 rocks of the Waen-Fechan intrusion, which represents a deep-seated 

 ^differentiation-product of the granophyre magma (pp. 290 & 297). 

 ^Similar rocks which originated in a similar manner, are found asso- 

 ciated with part of the margin of the Buttermere and Ennerdale 

 granophyre, and also as small separate intrusions near the main 

 granophyre, 1 exactly comparable with the Waen-Fechan and 

 'Tyn-jr-llwyn intrusions which will be described below. Similarly, 

 phasic rocks occur again along the margin of the Carrock-Fell 

 ..granophyre. 3 



(2) The Minor Granopli3 T ric Intrusions. 



In addition to the main Crogenen sill just described, there are 

 .some four (or five) smaller intrusions of granophyric rocks. 

 They consist for the greater part of rocks that are consanguineous 

 with, but more basic than, those of the main sill. These minor 

 intrusions all occur north or north-east of the main mass, and not 

 ■at any other points along its course, thus giving additional support 

 to the hypothesis of a north-easterly point of origin for all the 

 granophyric rocks (p. 286). They show, moreover, that there was 

 •some tendency for the intrusions as a whole to assume a form 

 ■compai-able with that of a cedar-tree laccolite. In this respect the 



1 E, H. Kastall, Q. J. G. S. vol. lxii (1906) p. 268, 

 - A. Harker, ibid. vol. 11 (1895) p. 134. 



