TRIASSIC BRECCIAS AND CONGLOMERATES OF SOUTH DEVON. 81 



the existing remnants of the felspathic traps by no means indicato a 

 capacity to supply ; and beyond the Dartmoor area we seek in vain 

 for a source of sufficient magnitude. And it will be borne in mind 

 that on the most moderate estimate an enormous amount of super- 

 incumbent matter must have been removed from Dartmoor before 

 its 300 square miles of granite could have been exposed as we see 

 them to-day, and that it is as absolutely certain as any geological 

 hypothesis can be, that a large proportion of this must have gone to 

 build up the beds of the adjacent Trias. 



Conclusions. 

 My conclusions may be summarized as follows : — 



1. That the igneous materials of the Triassic breccias and con- 

 glomerates of South Devon are, as well as the sedimentary, of local 

 origin. 



2. That they consist of granites, felsites, and volcanic types, 

 ranging from andesites to basalts. 



3. That the granites are wholly, the felsites mainly, identifiable 

 with the granites and el vans of Dartmoor and its borders. 



4. That the great bulk of the volcanic rocks are undistinguishable 

 in character from " felspathic traps " associated in situ with the 

 South-Devon Trias, but that andesitic features predominate. 



5. That schorlaceous and contact- altered rocks occur in the 

 breccias and conglomerates, which may be referred with absolute 

 confidence to the outer (or upper) zone of Dartmoor. 



6. That the few examples of igneous rocks in the breccias and 

 conglomerates which, allowing for alteration, cannot be absolutely 

 assigned to rocks yet existing in situ in Devon, are rocks of precisely 

 similar character, such as it is natural to expect in the same asso- 

 ciation, and simply phases of the same magma. 



7. That the condition under which the " felspathic traps " of 

 Devon occur m situ, their characteristic association with el vans, and 

 the part which they bear in the constitution of the Triassic breccias 

 and conglomerates, are calculated to lead to the inference that they 

 are volcanic phenomena connected with the igneous activities of the 

 Dartmoor region, and probably represent its final period, as the cpi- 

 diorites and proterobases of the north and west of Dartmoor may its 

 earlier stages. 



8. That the elevation of Dartmoor and the associated igneous 

 phenomena, which have been commonly regarded as post-Car- 

 boniferous and pre-Triassic, may in all probability be assigned to 

 narrower limits, and be regarded as not earlier than Permian times, 

 and possibly as occupying the Permio-Triassic interval, continuing 

 into the earlier stages of the Trias. Certainly if the eruptions of 

 the " felspathic traps " of Devon and their associated elvans are 

 related to the great Dartmoor movement (and, as we have seen, these 

 traps are in part of Triassic date), we cannot well give the origin 

 of that movement a higher than Permian antiijuit}. 



Q.J.G.S. X®. 181. " G 



