13 G MR. J. morrtsox on [vol. lxxiv, 



acid xenocrysts in diminishing amount. The magma yields rocks 

 the characters of which depend on two factors : the abundance of 

 xenocrysts and the composition of the matrix, a decrease in the 

 one and an increased basicity in the other marking the successive 

 stages. The more acid have affinities with the porphy rites, the 

 more basic with the lamprophyres, all being more or less modified 

 in composition by the presence of the xenocrysts, a hybrid series 

 being the result. 



From the magma which gave rise to these mixed products came 

 also the basic patches of the granite. They themselves show 

 varying degrees of basicity, and the scarcity of large felspars is 

 accompanied at times by a higher density. The basic patch of the 

 Wet Sleddale dyke is of interest in this connexion. Its density is 

 greater than that of any granitic patch that has been tested, and 

 it probably comes from a lower source. That an intrusion more 

 basic than the granite should be able to tap a lower portion of the 

 reservoir is only to be expected. It may be inferred, therefore, 

 that the granite in its passage involved portions of the underlying 

 magma which consolidated as basic patches, the same magma 

 giving rise to the mixed series of intrusions, some of which in their 

 turn involved portions of a still lower and more basic magma. 

 From the intimate association of the granitic and underlying 

 magmas one might expect a similar close connexion between their 

 products. This is actually the case. The first set of minor 

 intrusions, apart from one or two which may be regarded perhaps 

 as direct apophyses of the granite, consisted of the mixed series. 

 How long a period elapsed prior to their injection is uncertain. 

 Possibly they were intimately connected with the granite in time 

 as the}" are in space. The upper and more acid were injected north 

 of the granite mass, the lower and more basic on the south, while 

 their restriction to the immediate neighbourhood of the granite 

 is consistent with the above deduction. 



The abundance of porphyritic felspars in the granite, together 

 with its basic character, may be regarded as an indication that 

 the exposed mass represents the lower part of the original magma. 

 This proposition is more or less speculative ; but it is supported 

 by the presence of the basic patches. Dr. Harker & Prof. Marr 1 

 state that the amount of metamorphism would suggest the passage 

 of molten material through the channel for a considerable 

 period. It is a reasonable supposition that the differentiation 

 believed to have extended downwards from the mass exposed 

 extended upwards in the mass removed. The latter would be more 

 acid and probably less porphyritic, having lost some of its first- 

 formed elements by sinking. First to be intruded, or extruded, it 

 would be removed by the continued now, the less acid portion 

 coming last, consolidating in its present position, crowded with 

 felspars, and containing numerous basic patches. This would 

 partly acccount for the greater basicity of the Shap granite, as 

 compared with the Skiddaw granite of probably the same age. 



1 Q. J. G. S. vol. xlvii (1891) p. 292. 



