part 2] GEOLOfiY OF THE MELDON VALLEYS. 01 



Sourton Tors, but the exposures have not been worked out in 

 detail.) 



Assuming the average dip of the shales between LXXVI, 

 S.E. 31) and the L. A: S.W. Railway quarry to be 50° (and this is 

 a close approximation), then nearly 2000 feet of strata intervene 

 between the first and last above-recorded exposures of 'dark 

 igneous' rock, and in this thickness there is apparently no repetition. 



The Field-Relations of the 'Dark Igneous * Series and 

 the Shales. 



From these various exposures the following information may be 

 derived as to the relations existing between the shales and the 'dark 

 igneous ' series. In one instance the ' dark igneous ' rock forms a 

 definite sill, and might be interpreted as conformably interstratified 

 (LXXVI, S.E. 59), were it not that it sends apophyses into the 

 neighbouring shales, some of which apophyses, meeting radiolarian 

 cherts, have softened them and make contact on a wavy junction. 

 Another exposure is possibly in part a sill (LXXVI, S.E. 70-68), 

 but this when traced eastwards between 75-71 sends off at 15 

 a branch, which makes with the main belt an angle of 2-i° ; 

 ■obviously either the main belt or its offshoot must break across the 

 bedding of the shales: it is probably the offshoot ]5-7S, and not 

 the main exposure 71—75, that crosses the bedding. At LXXVI, 

 S.E. 39, we may be dealing with a sill ; but the evidence is not 

 clear. None of these sills show any passage-bed between the 

 aggiomeratic rock, of which each is in part composed, and the 

 shales either above or below. If the agglomerates were in fact 

 tuffs, then, if subaqueous in their origin, there should be passage- 

 beds, at least on the undersides, since the materials of these 

 relatively coarse agglomerates could not fall, even through water, 

 so gently as not to disturb the deposits on which they descended. 

 This absence of any commingling would be conceivable in a sub- 

 aerial tuff, but then there must certainly be unconformability — one 

 cannot imagine, awaiting the reception of the ashes, a rock-surface 

 which should be bare and at the same time precisely coincident 

 with an original bedding-plane. In the definite sills there is no 

 such unconformability. 



But, in addition to the sills, there are undoubted dykes which 

 do not conform to the dip of the shales. At LXXVI, S.E. 56, the 

 igneous rock appears to intersect the contorted shales uneont'orm- 

 ably. LXXVI, S.K. 58 strikes with the shales; but, while their 

 dip is ">() J north-westwards, the dyke dips 68° south-eastwards. In 

 places it has yielded homogeneous rock, elsewhere it has been aggio- 

 meratic. It has already been noted thai either7J 75 or 15— 78 must 

 cross the bedding of the shales. LXXVI. S.E. 84 (57 66 10 S2 

 breaks across the strike of the shales from (17 to 84. This rock is 

 a dolerite. and no part of this dyke has yet been proved to be 

 aggiomeratic. The exposure north and south of LXXVI, S. E. 2"> 

 is certainly out of accord with the bedding of the adjacent shales ; 



