08 MR. E. H. WOEXH OX THE [vol. lxxV, 



That intrusive rocks may take up fragments of the sedhnentaries 

 through which they pass is certain: an instance long since observed 

 is the elvan at Pentewan, near St. Austell, in Cornwall, which is 

 loaded with slate-fragments. That they may take up inclusions of 

 prior consolidations of their own magma can be asserted on the 

 evidence of the Dartmoor granite itself. Thus at Eedlake, in the 

 Erme Yallev, I sank a shaft in solid granite adjacent to a kaolinized 

 area, at CXIII, S.E. 11, long. 3° 54' 32", lat. 50° 29' 7". This, 

 on the Geological Survey map, appears to be some 2j miles distant 

 from the nearest sedimentaries. But, as always where any con- 

 siderable area of kaolinized granite exists, we are near the original 

 surface of that rock, proved in this case by an adjacent inlier of 

 sedimentary rocks on Brown Heath, not marked on the Survey 

 map. At a depth of 120 feet the granite contained big inclusions, 

 measuring up to 5 inches in length, of highly-metamorphosed 

 slate, and in addition equally big inclusions of its own chilled 

 margin, a microgranite, which itself showed inclusions of slate. 

 Both sorts of inclusion are sharply denned and clearly bounded. 



If these conditions are to be found in a plutonic rock, then an 

 enquiry into the credentials of any apparent tuff which deviates 

 from the normal would indeed seem necessary. 



Epidiorite (?) . 



An epidiorite occurs within this area ; it has not been found in 

 sitv, but between LXXYI, S.E. 5 & 6, near Anthony Stile, 

 surface-boulders are sufficiently frequent to indicate that this must 

 be the approximate location of a dyke. The rock is dark green- 

 grey. Slide 5 shows felspar, very completely saussuritized, 

 actinolitic hornblende, and large forms of ilmenite ; the felspar- 

 occurs in lath -prisms. In slide 6 the form of the felspar is pre- 

 served, but it is subdivided into smaller areas, and the mineral 

 is remarkably clear. Obviously it has been reconstituted : it may 

 now be an acid labradorite. The actinolite is as in 5, and the 

 ilmenite is in more skeleton form. Ko augite nor apatite occurs in 

 either slide. At Sourton Tors C. A. McMahoh described certain 

 epidiorites (-5, p. 340) : these, as shown in my sections, are finer- 

 grained rocks with less hornblende. 



VI. The Meldox Aplite. 



I use the term ' aplite ' with some reserve, and solely because 

 it has frequently been applied to this rock and has become 

 familiar ; a more accurate, if more cumbersome, description would 

 be ' lepidolite-soda-granite.' 



The typical Meldon aplite is not confined to one dyke: but. since 

 its geography has never been adequately dealt with, it might be 

 as well to refer first to the northernmost or main dyke. 



De la Beche's survey shows two isolated patches — the one on 

 the liedaven and the other on the Okement. As late as 191-3 



