214 THE SKOMER, VOLCANIC SERIES. [Mayi()II, 



ago as 1881 by Frank Butley, from specimens collected by Sir 

 Andrew llamsay. Though the question did not lie strictly within 

 the scope of the present paper, he would like to ask the Author 

 whether he had come to any definite conclusion as to the source 

 of the foreign boulders of hornblende-bio tite -granite found on 

 Skomer. 



Mr. E. P. Gwinnell asked whether it was not desirable to use 

 the term ' iime-bostonite,' or even the more definite name of 

 * maenaite,' as introduced by Prof. W. C. Brogger, in place of the 

 very vague term ' keratophyre,' for the rocks which the xluthor 

 described as being identical with lime-bostonite. 



The President (Prof. Watts) called attention to the presence of 

 olivine in the dolerites and basalts of the Skomer area — an unusual 

 feature, so far as his experience went, in rocks of this age. He 

 did not recognize, in the slides exhibited by the Author, any great 

 resemblance between the bedded volcanic rocks and those of the 

 zone of Didymograptus murchisoni on the Welsh borders. This 

 difference might, perhaps, be accounted for by the different age of 

 the Skomer rocks. 



The Author, in reply, thanked the speakers for their appre- 

 ciative remarks. With regard to the granite-boulders mentioned 

 by Mr. Small, he considered that they, in common with many on 

 the mainland of Pembrokeshire, derived their origin from the South 

 of Scotland ; they were associated with other rocks of Scottish 

 derivation. The term ' keratophyre ' had been used by him for 

 certain rocks, classed as such by Rosenbusch in his most recent 

 work ; but he recognized that it was an ill-defined rock-group, and 

 far too elastic to be of much classificatory value. He had not used 

 the rock-name ' lime-bostonite ' for these rocks, as their structure 

 was not bostonitic, and also it seemed unadvisable to use the name 

 4 bostonite ' for extrusive rocks. 



