part 2] GEOLUUV OJf THE MBLDON VALLEYS. Ill 



eastwards is made evident by aplite found as a vein in 'dark 

 igneous ' rock at LXXVI, S.E. 7. 



Some one or more of these dykes or sills would appear to 

 have a considerable south-westerly extension: a patch of boulders 

 amounting to an outcrop exists at LXXVI, S.E. GO, and a single 

 boulder at LXXVI, S.E. 61, both on Longstone Hill. 



Following the line thus indicated, we rind two dykes crossing 

 the bed of the Flushcombe, LXXVI, S.E. 8, and LXXVI. S.E. 62 : 

 the latter is 5 feet wide or thereabouts, strikes with the shales, but 

 dips counter to them ; it is accompanied b} r narrow veins of similar 

 rock parallel to it. LXXVI, S.E. 8, is about 18 inches wide and 

 strikes with the shales, but dips counter to them. 



At the foot of Homerton Hill, LXXVI, S.E. 38, are stones 

 and boulders which have been shed by a dyke cropping out on 

 the hill, at and about the 1000-foot contour. The mica in this 

 dyke shows pleochroic halos of two orders of dimension. 



The westernmost exposure that I shall mention is at LXXVI, 

 S.E. i) e, a shale-quarry in the Vellake Valley, hard by the stream. 

 The rock contains orthoclase, microperthite, and albite, and is 

 coarser in texture than the main dykes. There is a very little 

 white mica. The quartz is zoned with pale-brown dust : cavities 

 are numerous but small, some are empty, some have fluid and a 

 bubble. The tourmaline is brown, with blue pleochroic halos. The 

 topaz is quite fresh, shows good basal cleavage, and the biggest 

 crystal is about 5^ mm. long. The exposure is a dyke, exact 

 width not ascertained, but not many feet ; angle between underlie 

 of dyke and dip of shales 45°. The shales, which are of the alu- 

 minous type, develop much andalusite at and near the contact. 



Another aplite-dyke is seen across the Kedaven at LXXVI, 

 S.E. 30 «; its width is perhaps several feet. The last dyke of 

 aplite on the Kedaven is at LXXVI, S.E. 31 ; it is something over 

 100 feet wide. 



There is at the Museum of Practical Geology, Jermyn Street, 

 London, a specimen of similar rock, labelled as occurring between 

 Row Tor and Sea rev Tor; this was mentioned by Kutlev (3) r 

 and is obviously referred to in the Dartmoor Memoir of the 

 Geological Survey (8, p. 40). It is hardly hypercritical to suggest 

 that the label is too indefinite for working purposes, the distance 

 between the points named being fully a mile, liutley, in 1889, 

 made search for an exposure in this locality ; I have since 

 quartered the ground on more than one occasion, but no trace of 

 the rock has been found. 



Omitting tins last, somewhat doubtful item, the veins and 

 dykes of Meldon aplite are roughly parallel one to the other, and 

 approximately parallel to the strike of the shales. They occur in 

 a belt a little over 1000 yards wide at its broadest, bounded, 

 except for some minor offsets, on the north- west by the main 

 dyke. About half the width of the aplite-belt overlaps the area 

 in which the 'dark igneous' series occurs, the other half lies- 

 towards the granite-mass. 



