476 H. S. JEVONS, H. I. JENSEN, T. G. TAYLOR AND C. A. SUSSMILCH. 



Compared with analyses of ordinary olivine basalts this- 

 rock is seen to be rather poor in alumina and lime, and 

 somewhat rich in soda and ferrous iron. In many respects 

 it agrees more closely with analyses of nepheline basanites, 

 and in some degree resembles those of monchiquites. 



Specimen A. 



This specimen was taken from the same locality aa 

 Specimen B. just described, but only 15 cm. (6 inches) from 

 the junction with the shales instead of 30 cm. (12 inches). 

 The rock is so similar to rock B that there is no reason for 

 describing it in full. It differs from B in having rather less 

 olivine and rather more labradorite. Well rounded frag- 

 ments of shale are more abundant, and the biotite seems 

 in this slide to be rather more abundant where shale has 

 been absorbed. A complete zone of ferro-magnesian 

 minerals — biotite, augite, and hematite — often surrounds 

 much absorbed pieces of shale. The shale fragments appear 

 under the microscope to be of very fine granular texture 

 and in colour a cloudy grey; between crossed nicols they 

 are opaque. 



Locality: Reservoir Quarry, about centre of main face, 

 a few feet below and to the right of the detached mass of 

 shale (see Plate XXXV). Obtained from 4| metres (15 

 feet) below the junction with the shales. 



Megascopic Description. Colour dark greenish-grey, 

 like the rest of the rock from this zone in the quarry. 

 Minerals — Augite and plagioclase are distinguishable in the 

 hand-specimen, aud flakes of biotite are also recognisable. 



Microscopic Description. Texture: Crystallinity, non- 

 crystalline. Grainsize variable, from about 0*3 mm. to 

 1*0 mm., average 0'6 mm.; fabric pilotaxitic, inclining 

 towards ophitic. 



