﻿508 PEOr. S. H. EETNOLDS 02f THE [N"0V. I908, 



similar conditions by Dr. Plett in the case of the Spalefield rock,^ and 

 with the pseudomorphs described and figured by Dr. H. H. Arnold- 

 Bemrose ^ from Potluck (north-west of Tideswell). Dr. Arnold- 

 iBemrose, who kindly examined one of my slides, agrees that the 

 resemblance to the Potluck pseudomorphs is very close, and 

 ^considers that the replacing substance is a mica-like mineral. 



The rock at (46), from near the junction of the dolerite and basalt 

 at the southern border, exhibits an interesting intermingling of the 

 two rock-types, as, while mainly basaltic, it shows many included 

 patches of doleritic material, passing with irregular ill-defined 

 boundaries into the basalt. Mr. Harker suggests a comparison 

 with the ' glomero-porphyritic structure ' of Prof. Judd.^ The same 

 feature is shown in the rock at the spot numbered 62. The rock 

 from (46) differs from all the others, in the fact that the abundant 

 olivine is in the main perfectly fresh (PI. LII, fig. 3). The rock 

 at (41) contains no olivine, and the augite shows separation of 

 magnetite as in (11). 



At the spot numbered 47, a beautiful rock-type of medium 

 coarseness occurs. Abundant serpentinized olivine, showing good 

 crystal-outlines, is present ; and the augite, although forming a few 

 phenocrysts, is mainly in the form of small and very fresh grains 

 filling the interstices between the felspars. 



Sections from the spots (54) and (16) near the middle of the 

 dyke and from (17) — a point near (16), although its precise position 

 was not recorded, agree in the fact that the augite, which is very 

 abundant, shows as a rule corrosion of its borders and much 

 separation of magnetite ; but, while at (54) and (17) no olivine is 

 present, at (16) it is abundant. 



At a spot very close to (17) a rock occurs, having a specific gravity 

 of only 2-69, and is to be grouped rather with the augite-andesites 

 than with the basalts. 



A section from (61), a point approaching the northern border, 

 shows an undulating line of junction between two sharply-defined 

 rock-types, basaltic and doleritic. The felspar-laths of the basalt 

 tend to accumulate along the line of junction with the dolerite and 

 to be arranged with their long axes parallel to the edge. The 

 character of the junction makes it clear, not only that the basalt 

 was a later intrusion than the dolerite, but that the dolerite was 

 completely consolidated before the intrusion of the basalt. An 

 interesting section comes from (19), a point at a distance of 6 feet 

 from the northern edge of the d5''ke. It consists in the main of 

 basalt, showing the usual augite with corroded borders and separation 

 of magnetite ; but the basalt includes patches of dolerite and also a 

 number of glassy patches which are dark, nearly isotropic, and 

 imperfectly variolitic. 



The occurrence of basaltic as well as doleritic material in the 

 immediate neighbourhood of the northern margin is shown by the 

 presence of a fine-grained basalt devoid of olivine at the points (31) 



^ Appendix to 'The Geology of EasternFife' Mem. Geol. Siirv.Scot.l902,p.S92. 

 2 Quart. Journ. Geol. Soc. vol. 1 (1894) p. 613 & pi. xxiv, fig. 3. 

 » iJerf. vol. ilii(1886)p. 71. 



