﻿Vol. 64.] THE BASIC INTRUSION OF BAETESTEEE. 505 



Two sections of this rock were examined. The first (6)/ passing 

 through the actual junction with the Old Eed, consists mainly of 

 fair-sized labradorite- crystals and augite completely altered into a 

 yellow, apparently serpentinous mineral, which wraps round and 

 encloses the felspars. No olivine occurs. Magnetite and leuco- 

 xenized ilmenite are both abundant, the latter occurring in small 

 irregular patches, the former in rather long crystals. The last 

 quarter-inch of the section in immediate contact with the Old Eed 

 contains a fair amount of calcite in irregular patches, and a little 

 quartz which was no doubt picked up from the Old Red ; the 

 felspars too are larger, fresher, and more abundant than in other 

 parts of the section. A section (7) taken 3 inches from the junction 

 with the Old Eed, while agreeing with that just described in 

 consisting mainly of labradorite and serpentinized augite, differs, 

 in the following respects : — there is no ilmenite, and the abundant 

 magnetite occurs chiefly in irregular grains instead of elongated 

 crystals ; needles of apatite are plentiful ; and pseudomorphs in 

 carbonate after olivine are abundant : these are of no great size, 

 about '5 millimetre being the maximum diameter. A third section 

 (49), taken from close to the junction with the Old Eed near the floor 

 of the quarry, shows further differences. No olivine, either fresh or 

 altered, occurs, a little biotite is present, small apatite-needles are 

 very abundant, and the iron-ore is chiefly ilmenite. In addition 

 to the presence, as in the two previous slides, of patches of ser- 

 pentinized augite, this mineral occurs abundantly in small, fresh, 

 brightly-polarizing grains, and forms also a few relatively-large 

 twinned crystals. 



(2) The prevalent type of doleritic rock is, however, a coarser- 

 grained dark-green rock, occurring principally near the southern 

 margin of the dyke, but also at various points near the centre and 

 the northern margin. It is a heavy rock, specimens from near the 

 southern margin giving a specific gravity of 2*84 to 2-88 and a silica- 

 percentage of 43" 03. In sections from two neighbouring spots (9 

 and 10) near the southern margin, olivine in a completely serpen- 

 tinized state, but sometimes showing good crystal-outlines, is one 

 of the most abundant minerals. These crystals are of considerable 

 size, sections sometimes showing a length of Ig mm. The augite 

 is all very fresh and polarizes brilliantly, being partly ' granulitic,' 

 partly in fair-sized non-ophitic crystals which do not show anj- sign 

 of pleochroisml The augite and olivine are by far the most abundant 

 minerals, the olivine in one section forming at least one-third of 

 the bulk of the rock. Small augite-granules polarizing with the 

 greatest brilliance are gathered together into nests, and in one case 

 form a band 2 to 3 millimetres broad stretching across the section. 

 Fairly fresh labradorite is plentiful, but does not play so important 

 a part as in the doleritic rocks previously described. Magnetite is 



^ The spots from which the sections indicated by the numerals in parentheses 

 were obtained are shown in the accompanying diagram of the quarry-face 

 (p. 504). 



