528 Geological Society. 



with the piping of the limestone-surface at Ebbsfieet and the 

 absence of Millstone Grit in Kent, tended to confirm the view 

 that there is unconformity between the Coal Measures and the 

 Carboniferous Limestone in that county. 



Mr. F. P. Mejstkell exhibited a geological sketch-map 

 of. the northern margin of Dartmoor. 



He said that the central part of Devon was to a great extent 

 a terra incognita ; but, as regarded the fringe of altered Carbon- 

 iferous rocks along the northern border of the Dartmoor granite, 

 he had been led, in the course of observations originally concerned 

 with the petrology alone, to the conclusion that it might prove 

 possible to establish a definite order of succession. This was 

 rendered feasible by the occurrence of some well-characterized 

 bands of rock, especially limestones and tuffs, which were exposed 

 in every good river- section. It was true that almost everywhere 

 overfolds, sometimes accompanied by thrusts, were to be de- 

 tected, and tended to make the observer somewhat doubtful of 

 his ground. Nevertheless, it seemed impossible to escape the 

 conclusion that, as one approached the granite from the north, 

 continuously older rocks were met with, and the extremely 

 continuous character of some of the beds seemed to show that, 

 despite all minor disturbances, the general sequence could be 

 trusted. The comparison of the different lines of section leading 

 up to Dartmoor showed them to be strikingly similar. The 

 granite was, moreover, intruded all along at precisely the same 

 horizon, and its direct offshoots never reached into the lower of 

 the two important bands of limestone, but were confined to the 

 altered shales at the bottom of the series, which afforded, where 

 fresh, good examples of andalusite-hornfels. The series, which 

 extends from south of Sourton to Drewsteignton and perhaps right 

 round to Doddiscombeleigh, appears clearly older than the shales 

 which have been so carefully searched for fossils in the Exeter 

 region by Mr. F. J. Collins. These last are considered to be of 

 Pendleside age, and nowhere contain any traces of limestone. 

 The probability is thus indicated that the distinctly calcareous 

 series under consideration may represent part of the Carboniferous 

 Limestone. 



It may be noted that, although a number of bands of epidio- 

 rite representing intrusions of dolerite occur roughly parallel to the 

 strike of the sediments, the contemporaneous rocks are never of 

 such basic character. The main band of tuff stretches from Lake, 

 near Bridestowe, to beyond Sticklepath, and, of the numerous 

 well-preserved rock-fragments that it contains, most are of 

 rhyolitic or trachytic character, with some which represent altered 

 andesites. 



