10 BONNEY : ON THE ORIGIN OF THE BRITISH TRIAS. 
English side of the Cheviots,* as well as in Scotland, and is not 
rare as a vein product and in a schistose slate in the Isle of 
Man, so it may have been more abundant in the rocks which 
disappeared in forming these Midland pebbles. The other 
difficulty is also serious, that the pebbles are more abundant 
in Staffordshire and its immediate neighbourhood than they 
are in the district round Liverpool. They are, however, more 
frequent there and of greater size than is sometimes supposed, 
but they are more largely mixed with sand, for the pebble 
bed as a whole is, as already stated, fully three times as thick 
in the latter as it is in the former district. Near Liverpool 
we seem, as I have more than once observed, to be out of the 
main course of pebble deposit and in that of sand deposit, so 
that the difficulties are to some extent antagonistic. I think 
they may be reconciled by supposing that in what is now Lanca- 
shire the main current of the river happened to occupy a nar- 
rower channel than it did in Staffordshire. 
Here, however, I have anticipated a little in speaking of a 
river, for some have considered the Bunter to be a marine 
deposit. But in that hypothesis one difficulty appears to me 
insuperable. Pebble beds formed by the sea are always limited 
in one of their three dimensions ; if thick they are narrow, if 
widespread they are shallow. The Bunter Pebble Bed in Stafford- 
shire is broad, and long, and thick. To this I may add that it 
presents a remarkable resemblance to the pebble beds formed 
by rivers issuing from mountain regions. For some 20 years 
I have paid considerable attention to the Alpine gravels. The 
Nagelfluhe — a Miocene deposit — resembles in many respects 
the Bunter gravels, and the Molasse, with its occasional seams 
of pebbles, is not unlike the Keuper sandstone. The Pleisto- 
cene or very late Pliocene Idcherige Nagelfluhe or Deckenschotter 
closely resembles the Bunter in mode of deposit and dis- 
tribution, but is a little coarser and more " tumultuous " in 
aspect, while the older Alpine river gravels, except that they 
are restricted to narrower cliannels, present a still closer 
resemblance. 
* Geol. Survey Memoirs, The Cheviot Hills (English Side), C. T. 
Clough (188S), p. 10. 
