part 2] THE GEOLOGY OF THE MELDOK VALLEYS. 



[5. The Geology of the Meldox Valleys near Okeiiamptox, 

 on the Nobthern Verge of Dartmoor. By Kictiard 

 Hansford Worth, M.Inst.C.E., F.G.S. (Read November 

 20th, 1918.) 



[Plates V-VIIL] 



Contents. 



Page 



I. Bibliography and Introduction 77 



II. General Structure of the Area 78 



III. The Shales 79 



IV. The Calcareous Series 82 



V. The Igneous Rocks 88 



VI. The Meldon Aplite 98 



VII. Granite Veins 112 



I. Bibliography and Introduction. 



(1) 1839. Sir Henry T. De La Beche, ' Eeport on the Geology of 



Cornwall, Devon, & West Somerset' p. 501. 



(2) 1888. Sir Jethro J. Harris Teall, ' British Petrography ' p. 316. 



(3) 1889. Frank Rutley, unpublished report made for commercial 



purposes. 



(4) 1893. C. A. McMahon, 'Some Notes on Dartmoor' Q. J. G. S. 



vol. xlix, p. 387. 



(5) 1894. C. A. McMahon, ' On Rocks of Igneous Origin on Dartmoor ' 



Q. J. G. S. vol. 1, p. 350. 



(6) 1895. R. N. Worth, ' Notes on the Geology of Okehampton ' Trans. 



Devonshire Assoc, vol. xxvii, p. 306. 



(7) 1901. Harford J. Lowe, Trans. Devonshire Assoc, vol. xxxiii, p. 112. 



(8) 1912. ' The Geology of Dartmoor ' Mem. Geol. Surv. pp. 38, 40, 47. 



The area covered by these notes comprises as much of the water- 

 shed of the West Okement and the Redaven as lies between the 

 London & South- Western Railway-line on the north and, on the 

 south, the 'Roof of Devon,' the Yes Tor-High Wilhays ridge; 

 practically it is yet further restricted, since but brief reference is 

 made to the granite-mass of Dartmoor. 



The rivers and brooks within this area have been useful section- 

 cutters in a country where, for many acres, stray boulders on grass- 

 land are the only other guides, and their assistance has been more 

 marked since the great Hood of August 14th, 1917, which not only 

 swept their beds clear, but tore away from the banks their cover 

 of grass and heather. 



Artificially, also, much has been done to reveal the rock-structure. 

 A very extensive quarry is worked by the railway company east of 

 Meldon Viaduct, the face of this quarry being some u'00 yards 

 long. Formerly limestone was raised south of the railway, both 

 on the eastern and on the western banks of the West Okement; 



