Vol. 56.] EARTH-MOVEMENT IN THE ISLE OF MAN. 25 



eruption that any signs of disturbance manifested themselves. The 

 eruption, moreover, was one of exceptional energy and extent, far 

 more so than the contemporaneous outbursts in Derbyshire and 

 Somerset, nor could we judge of its full extent, for one margin only 

 of the volcanic tract was visible above the sea. For these reasons 

 he was still disposed to attribute some of the structures described 

 to the tumult caused by the ejection of igneous material on the 

 sea-bottom ; but at the same time he congratulated the Author upon 

 his presentation of an excellent working hypothesis. 



Prof. Watts said that he had gone over the district described by the 

 Author, and was struck by the fact that the Carboniferous limestones 

 and tuffs both occurred in knolls and knobs apparently of precisely 

 similar structure. If so much earfch-movement had affected rocks 

 subsequently to the Carboniferous period, great caution must be 

 exercised in working out the structures of rocks of this date. He 

 referred to the intrusive clastic sills which occur in the South of 

 Ireland, at Berehaven and elsewhere. 



The Author, in reply, acknowledged the difficulty in distinguishing 

 between original and superinduced structures in rocks of this 

 character, and said that he had not ventured to assign the exact 

 proportion of the one to the other. But he claimed that the present 

 position of the limestone-lenticles showed that there must have been 

 great disruption and re-arrangement throughout the series. There 

 seemed no reason to doubt that the greater part of the ash had been 

 deposited in the sea. That the disturbance was so much more acute 

 in the volcanic rocks than in the limestone was probably due to the 

 heterogeneous composition of the former. The movement throughout 

 seemed to have been approximately from south to north, and 

 Prof. Blake's difficulty arose from the fact that the sections exhibited 

 were not all at the same angle in regard to the movement. He was 

 glad that Prof. Boyd Dawkins agreed that the Peel rocks had also 

 been disturbed, and regretted that they should still hold different 

 opinions as to the age of these rocks. He desired to thank 

 Prof. Watts for having stimulated the further research which had 

 led to the present results, by his friendly criticism when they were 

 together in the field. 



