﻿510 PEOF. S. H. EEYNOLD« ON THE [NoV. I908, 



Y. Conclusion. 



The rocks just described, though showing a large amount of 

 variation, are all closely related ; and the facts seem most readily 

 explicable on the view that, in the Bartestree dyke, we have evidence 

 of three successive injections of basic material. First, in all 

 probability, came the green dolerite without fresh or serpentinized 

 olivine, chiefly seen near the southern margin. Then followed the 

 darker, coarser teschenite, which (judging from the sharply-defined 

 junctions) was completely solidified before the intrusion of the basalt. 

 This latter rock formed the central and major portion of the dyke, 

 enclosing here and there patches of the teschenite, and further 

 sending veins into the marginal portion. The basalt-magma 

 brought up with it numbers of small ill-defined patches of coarser 

 material, and here and there portions of the magma solidified in a 

 glassy condition. 



As regards the date of the intrusion, all that can be learnt from 

 field-evidence is that it is later than the Old Eed Sandstone. The 

 strong resemblance of the dolerite to many of the other Midland 

 dolerites, and especially to the Clee-Hill rock, suggests that it belongs 

 to the same series, in which case it would not be earlier than very 

 late Carboniferous. 



Prof. Watts ^ remarks on the very close resemblance between 

 some of the Midland dolerites and some of those of Scotland and 

 the North of England, and suggests that the former group, like the 

 latter, may really be of Tertiary age. The presence of analcime 

 affords no indication as to whether the rocks are of Carboniferous 

 or of Tertiary age, this mineral having been met with in British 

 doleritic rocks of both these periods. In the non-pleochroic and 

 almost entirely non-ophitic character of the augite, the Bartestree 

 rock approaches more closely to the Carboniferous than to the 

 Tertiary dolerites. 



I wish to acknowledge my great indebtedness to Mr. Alfred 

 Harker, F.E.S., both for help in examining my sections, and for the 

 loan of sections of other analcime-bearing rocks. 



EXPLANATION OF PLATE LII. 



[The numerals in parentheses refer to the diagram, p. 504.] 



Fig. 1. Teschenite (51), near the southern margin of the dyke : X about 25. 



The large, roughly-triangular, clear patch in the left half of the 

 figure is analcime. The dark patch in the right-hand top corner 

 consists partly of serpentinized olivine, partly of magnetite. The 

 remainder of the section is occupied by labradorite-laths, apatite- 

 needles, and avigite-grains. (See p. 506.) 

 2. Olivine-dolerite (55), near the middle of the dyke: X about 25. 



This shows several completely-serpeutinized olivines, vrith numerous 

 labradorite-laths and augite-graius, the latter being best seen near 

 the base of the figure. (See p. 507.) 



1 Proc. Geol. Assoc, vol. xv (1898-99) pp. 399-400, & ibid. vol. xix (1905- 

 1906) pp. 178-80. 



