Miss I. H. Lowe — Igneous Rocks of Ashprington. 353 



filled with quartz, chalcedony, calcite, and haematite. The red and 

 brown colour of the rocks in the area is especially characteristic of 

 those exposed in road cuttings and old disused quarries. The specific 

 gravity of the fresher specimens varies from 2 - 87 to 2 - 98. 



The" rocks are cleaved and generally show curved irregular joint 

 planes; but typical "pillow structure", such as that developed in 

 the spilite in Chipley quarry and described in the Newton Abbot 

 Memoir (p. 54), is only shown in one exposure in a small road 

 cutting just outside Cornworthy village. A large pillow is exposed, 

 showing numerous small vesicles arranged in concentric bands; the 

 material of which it is formed is dark brown, but is too rotten to 

 allow of microscopic examination. 



Narrow veins are abundant in all rocks, frequently intersecting and 

 crumpled or faulted. The minerals filling the veins are quartz, 

 epidote, chlorite, actinolite, asbestos, and calcite. 



-^ 



FlG. 2. — Diagram illustrating the arrangements of the coarse fragments in the 

 crag at exposure XXVII. 4 = imbedded fragments, B = the cavities 

 resulting from the weathering out of the fragments. Continuous lines 

 represent the direction of the cleavage planes. Broken lines represent 

 the bands along which the fragments are arranged. 



One of the least decomposed of the diabases is that exposed in 

 a quarry at Stancombe Linhay, two miles south of Totnes. When 

 examined under the microscope the rock was seen to be sub-ophitic 

 and to contain fairly large, fresh, pale puce-coloured crystals of 

 augite, which are irregular in shape, slightly pleochroic, and are 

 abundantly penetrated by very small lath-shaped felspars. In most 

 of the diabases the augite is only recognizable under a J in. 

 objective. They are all noticeably rich in felspar, which must have 

 been originally the most abundant constituent of the rock. Most 

 rocks show two generations of felspar; those of the earlier are well- 

 formed phenocrysts, the sections of which are elongated and 

 rectangular or rhombic in shape. Some of the felspars show 

 evidence of corrosion, having rounded angles, and in the rock from 

 Down's Hill quarry containing devitrified glass inclusions. The 

 crystals vary in size, from microscopic to large macroscopic, one in 

 a specimen from Austin's Close quarry measuring 85 sq. mm. The 

 felspars of the second generation are small and lath-shaped ; in the 

 ophitic diabases they penetrate the augite, and in the non-ophitic types 



DECADE VI. — VOL. VI. — NO. VIII. 23 



