8 BONNEY : ON THE ORIGIN OF THE BRITISH TRIAS. 
spending with this is the comparative rarity of the almost 
vitreous quartzites of the Midlands, those common at Budleigh 
Salterton bearing a general resemblance to quartzites such as 
I have seen in the Gorran Haven district. Tourmaline-bearing 
grits are, I think, more common, often in rather larger and 
more rectangular pieces than in Staffordshire, but the felstones 
are less abundant ; the very characteristic rocks of the Lizard 
peninsula, with the granites of Devon and Cornwall and the 
Devonian limestones, so far as I could see, did not occur. 
Such pebbles as I have examined from the Keuper, when not 
of local origin, as in the breccias, correspond with those in the 
Bunter, being usually quartzites and vein-quartz, and are seldom 
large. They prove, however, that the source from which the 
latter may have been derived continued, though more sparsely 
and intermittently, to supply materials until the setting in of 
the Red Marl. 
We must not, however, forget the smaller clastic materials. 
The Bunter sandstones of the Midlands are largely composed 
of quartz, stained externally with ferric oxide. In the upper and 
lower divisions well-rounded grains, as I have said, are abundant 
at certain horizons, but they are less common, so far as I have 
seen, in the matrix of the pebble bed. Grains of iron oxide 
may be observed, and no doubt rarer minerals will be found if 
sought for. Mr. H. H. Thomas has shown by his admirable 
investigation of the sands in the Devonshire Pebble Bed how 
rich a harvest awaits the investigator,* Among its rarer minerals 
he found garnet, anatase, rutile, zircon, apatite, brookite, silli- 
manite, staurolite, cyanite, and titanite, with micas and felspars, 
besides fluorspar, cassiterite, and tourmaline. These suggest a 
derivation from rocks, the representatives of which still occur 
in southern Cornwall and may now be concealed beneath the 
waters of the English Channel. f It is noteworthy that nearly 
all those in the first-named group, together with tourmaline, 
have been detected by Mr. A. B. Dick and others in the Lower 
Bagshot sands (at Hampstead), the materials of which are 
generally supposed to have travelled from the south-west. 
* Quart. Jour. Geol. Soc, Iviii. (1902), p. 620. 
t See W. A. E. Ussher, Q.J.G.S., xxxv. (1879), p. 245. 
