Vol. 56.] THE SOUTH-EASTERN COAST OF JERSEY. 31i> 



diabase) and plagioclase, but occasionally containing augite. The 

 two rocks are probably closely related. 



(ii) These were brecciated by a more acid magma, represented by 

 a rock containing plagioclase and some orthoclase, but poor in 

 quartz, hornblende, and mica, with the result that considerable 

 mixing took place. 



(iii) The result of this mixing was to produce a rock character- 

 ized sometimes by a gneissose structure, at others by elongated 

 hornblendes, occasionally of large size. Mica is conspicuously 

 absent. 



(iv) A further intrusion of a still more acid magma followed, 

 which solidified as a granite very closely resembling the earlier 

 porphyritic intrusion of Sorel Point. 



(v) This produced locally, by mixture, rocks which may be said 

 to be distinguished by the presence of biotite, quartz, and the 

 characteristic orthoclase of the granite. 



(vi) To these succeeded another intrusion of the acid magma, 

 forming a rock redder in colour, finer in grain, sometimes micro- 

 pegmatitic, and closely related to an aplite. This is typically 

 developed in the Western District round St. Elizabeth's Castle, and 

 is correlated with the second intrusion of the acid magma at Sorel 

 Point. 



(vii) A process of absorption and mixture again resulted; and 

 the penetration of the diabase by quartz and felspar (carried often 

 to an unexpected degree) leads me to suggest the possibility of 

 those minerals being introduced by hydrothermal agencies. 



(viii) Evidence in the field and with the microscope is brought 

 forward to show that the difference in age between these various 

 rocks was probably not great, and it is accordingly suggested that 

 they may have been differentiated from a single magma. 



So far as it goes, the evidence afforded by the rocks of Guernsey 

 bears out the sequence of intrusion described in this paper. 



Finally, I wish to acknowledge the help afforded by Prof. 

 Bonney, not only in study with the microscope, but also in the 

 theoretical questions which arose during the investigation. 



