BONNE Y : ON THE ORIGIN OF THE BRITISH TRIAS. 9 
What inductions then, as to the physical geography and 
chmate of the British Trias, follow from these facts of distribu- 
tion and petrographic character ? In the first place, as I have 
already said, the history of the Bunter is one thing, that of the 
Keuper another. Assuming that the Pennine Range existed 
throughout the Trias, I proceed to inquire whether the materials 
of the Mid-England Bunter came from a northern or a southern 
direction. The former inference is supported by the gradual 
thinning out of the three members as they are traced from 
South Lancashire towards a line which may be drawn from 
rather north of Worcester to Leicester, and on the whole by 
the petrography of their materials. For the abundant sand 
we may look to more than one source in Scotland, augmented 
by the grits of Carboniferous age in the Pennines. Xo other 
source of supply is visible ; the Old Red Sandstone of South 
Wales mostly lies too far to the south-west ; only slight hints 
have been found of any similar rock beneath Mesozoic deposits 
to the south-east of the above-named line ; the vein-quartz 
pebbles help us little, for that rock occurs in so many places ; 
the more characteristic quartzites do not closely resemble any 
exposed in Wales, Shropshire, or Warwickshire, but are exactly 
like those which occupy large areas in North-western Scotland 
and are abundant to the south of it in the Old Red conglomer- 
ates. The same may be said of the quartz-felspar grits ; 
they are exactly like the Torredonian which underlies that 
quartzite and do not so closely resemble that of the Longmynd, 
which in Triassic times cannot have occupied a much larger 
area than it does now. The felstones also can only be identified 
in Scotland, where many of them occur abundantly both i7i situ 
and as pebbles in the Old Red Sandstone conglomerates. 
But this h3rpothesis of a northern derivation of these Bunter 
pebbles involves two difficulties. One is the not unfrequent 
occurrence of tourmahne in felstones, quartzites, and vein- 
quartz. This mineral is abundant in the south-west of England, 
from which general direction I have no doubt the South Devon 
Pebble Bed derived its materials, but it is very rare in the north. 
It has, however, been found by Mr. C. T. Clough in vein-stones 
and in pebbles of an Old Red Sandstone conglomerate on the 
