﻿598 



ME. J. V. ELSDEN ON THE IGNEOUS EOCKS [Aug. I905, 



area, protruding in a marshy field about half a mile west of the 

 farmhouse. I believe that the rock is in situ, and its occurrence at 

 this horizon would then tend to confirm its intrusive origin. It is 

 possible that these brecciated intrusions have been produced by earth- 

 movements, in a man- 

 ner somewhat similar 

 to those described by 

 Mr. Lamplugh in the 

 r^ Manx Volcanic Series, 1 

 § a conclusion which is 

 £ strengthened by the 

 ll fact that a good deal 

 I of folding is noticeable 

 ij in the cliff- sections 

 a, near Abercastle. 

 £ Several of the paral- 



J lei sills lying between 

 *2 Abercastle and Mathry 

 r| are of the same type 

 & as the Pwll-Whiting- 

 J£ Abercastle intrusion. 

 ^ Specimens from Car- 

 n § nachen Wen (PI. XL, 

 O ^f fig. 2) and from an 

 ~ 2 exposure in the Aber- 

 § castle road, about a 

 g mile from Mathry 

 « (PI. XL, fig. 4), are 

 "£ petrographically iden- 

 "S tical with the lime- 



CD 



1 bostonite of Aber- 

 §" castle, with the excep- 



2 tion of a greater pro- 

 a portion of porphyritic 

 § felspars. I noticed no 

 g sign of brecciation, 



"-§ however, in these 

 8 areas. 



_g A somewhat dif- 



£-> ferent type occurs at 

 Cwm-y-Graig, near 

 the south-eastern ex- 

 tremity of Mathry Hill, 

 where a conspicuous 

 boss of pale-blue compact rock is quarried for road-metal. Micro- 

 scopically, this rock differs from the type described above, in having 



1 ' On some Effects of Earth-Movement on Carboniferous Yolcanic Rocks of 

 the Isle of Man' Quart. Journ. Geol. Soc. vol. lvi (1900) p. 20. 



