﻿94 



ME. Gt. W. TYRRELL OK THE 



[vol. lxxii, 



Fig. 3. — Geological map and section of a part of 

 tJie Lugar Sill. 



[P = Picrite and peridotite ; T = Teschenite ; Th. = Theralite.] 

 (4) Summary. 



It is now possible to attempt a general view o£ the Lugar sill, 

 and of the structure and disposition of the various facies of which 

 it is composed. This mass, 140 feet thick, was intruded into cold 

 rocks, as testified by the chilled contacts at both upper and lower 

 margins. The upper and lower contact-basalts are identical in 

 composition. The chilling influence of the contact is manifest in 

 fineness of grain to a maximum thickness of 10 feet, after which 

 the rock passes rapidly into a coarse teschenite at both margins. 



