SIMPSON ! STRATA AND DEPOSITION OF THE MILLSTONE GRITS. 419 
The Rough Rock in its persistence over a really large area and 
consistency of texture, can scarcely be accounted for by ordinary 
stream or estuarine conditions. It was probably first piled in bars or 
banks of sand by the laden streams, and afterwards, either by changing 
currents or further subsidence, washed down and redistributed over 
the extensive area it covers. 
It would be extremely interesting if we had more direct evidence 
as to the ancient rocks that furnished the material for our grits. 
It is hard in the very nature of the case to get any reliable evidence 
from the current bedding as to the directions of the streams ; in such 
shoaly tracts the currents were almost necessarily in all and variable 
directions. Jukes-Browne adduces evidence that some, at any rate, 
of the materials were derived from the central island he delineates. 
Dr. Sorby, in a pamphlet on the structure and origin of the 
Millstone Grit of South Yorkshire, says, " I have made an extensive 
series of observations of the direction of the currents present during 
the deposition of the Millstone Grit, as indicated by the drift-bedding 
over a district twenty-five miles long in South Yorkshire and North 
Derbyshire, and I find that on an average the current was from the X.E. 
This also agrees with the direction in which the sandstone beds grow 
thicker and coarser;" and, in further proof of his deductions, Dr. 
Sorby describes the finding of undoubted granitic pebbles, which, on 
comparison, are extremely like some of the Scandinavian rocks whilst 
unlike those of any British area. 
Professor Bonney has examined a piece of Carboniferous grit 
from near Cleveden (Somersetshire), and from the quartz grains and 
fragments of fine-grained micaceous schist was inclined to trace its 
origin to the minutely crystalline schists of Anglesea. 
It is highly probable that both the rivers of the continental area 
to the north and east, and the streams from the central island in 
the west and south of our district, helped to swell the mass of 
mechanical sediment composing the rocks of this series. 
It would have been extremely interesting too, to have considered 
the later earth movements that have so uplifted, broken, and faulted 
these rocks, and that have resulted in exposing as our surface rocks 
measures that must at one time have been covered by some thousands 
of feet of Coal Measure strata. 
K 
