242 ME. H. H. THOMAS OJs T THE [Aug. I909, 



Prom a study of the distribution and quantity of certain mineral 

 species, it is possible in most instances to gather some idea of the 

 relative amounts of material derived from various sources. This is 

 more especially true in the case of the Lower Breccias and Sandstones 

 and the Pebble-Bed. The material forming the marls, however, as 

 might be expected from its finely comminuted nature, appears to 

 have been supplied from all directions, and by a greater variety of 

 rocks than those yielding detritus towards the formation of the 

 other New Ped sediments. 



With regard to the source of the various mineral species it is 

 most difficult to speak, except in certain cases ; but, so far as can be 

 judged, all the minerals detected in the New Ped deposits, with the 

 exception of staurolite, could be supplied by the older rocks of the 

 West of England. The greater abundance of such minerals as blue 

 tourmaline, topaz, rutile, and brookite appears to indicate that the 

 rocks in which they occur were largely derived from the granite- 

 masses of Devon and Cornwall, but more especially points to their 

 attendant metamorphic rocks and veinstones. 



The garnets of the New Ped deposits are clearly in no way 

 dependent on the distribution of staurolite, but, on the contrary, are 

 of most frequent occurrence in the northern part of the district 

 where staurolite is less abundant. The fact that garnet, in the 

 Pebble-Bed, makes its appearance together with an increased pro- 

 portion of blue tourmaline, points to its derivation, at any rate in 

 part, from the metamorphic rocks surrounding the West of England 

 granites. Its absence from certain horizons might be accounted for, 

 either by the direction of the sediment-bearing currents, or by the 

 extremely local occurrence of garnets in the metamorphic aureoles 

 of this district. It is only where subordinate calcareous bands of 

 the Devonian and Carboniferous rocks and diabase-intrusions come 

 within the influence of the granites that this mineral has been 

 produced. It is not suggested that all the garnets in the New 

 Ped rocks were supplied by these metamorphic areas ; but, should 

 it be so, it would appear from the distribution of this mineral 

 that all the New Ped rocks of North Devon and West Somerset 

 were formed in part of material carried from the west and south- 

 west. 



The Lower Breccias have always been considered as deposits 

 derived from sources near at hand, for, as pointed out b)~ De La 

 Beche, Godwin-Austen, Conybeare & Phillips, and Mr. P. H. Worth, 

 among the rock-fragments found in them are numerous examples 

 of well-known rock-types present in Devon. The minerals and 

 grains forming the finer material of these deposits point towards 

 the same conclusion ; but, in addition, especially in South Devon, 

 they suggest strongly the influence of certain rock-masses non- 

 existent within the south-western area as now known. There is, 

 also, nothing in the finer material to prove that the granite-masses 

 themselves were undergoing denudation at the time when the 

 Lower Breccias were being deposited. 



