566 Geological Society. 
as in the Silurian and Cambrian systems, which from their lithological 
characters have been mistaken for “‘ greywacke,” the use of that word 
as expressing the age of rocks is no longer consistent with the ad- 
vanced state of geological science, and that if used, the name should 
either be rigidly restricted to some of the very oldest sedimentary de- 
posits, or simply employed as a mineralogical definition of peculiar grits 
which actually reoccur in strata formed in many succesive epochs. 
Feb. 3.—A paper on “ The Gravel and Alluvia of S. Wales and 
Siluria as distinguished from a northern drift covering Lancashire, 
Cheshire, N. Salop, and parts of Worcester and Gloucester,” by R. 
I, Murchison, Esq., V.P.G.S., was read. 
The first part of this memoir describes the detritus in the Welsh 
and Silurian territories, The surface of this region is completely 
exempt from the debris of any of those far-transported rocks which 
constitute what has been called ‘‘diluvium’”’ in other parts of England; 
all the loose materials in S. Salop, Herefordshire, and the adjoining 
Welsh counties having been derived from the Silurian and trap rocks 
of the adjacent mountains. These mountains range from N.E. to 
S.W., presenting inclined planes to the S.E., on the surfaces of 
which the broken materials are distributed. Four of the rivers which 
descend from the higher parts of Wales flow to the S.E. in accord- 
ance with the prevailing lines of drift, traversing the ridges of Silurian 
rocks through fissures which have resulted from dislocations of the 
strata. These are the Teme, the Onny, the Lug, and the Wye, all 
tributaries of the Severn. That great river, on the contrary, does not 
follow the “ line of drift” to the S.E., but escapes from the mountains 
to the north by a lateral gorge under the Breidden Hills; and after 
a circuit in the Vale of Shrewsbury passes eastward through a narrow 
transverse rent in the upper Silurian rocks and coal measures of Coal- 
brook Dale; and taking its final course southward, from Bridgnorth 
to the Bristol Channel, forms the eastern limit of the country covered 
by the Welsh or Silurian detritus. The drainage of the Teme, Onny, 
Lug, and Wye, is described in detail, with a view of showing, that in 
the valleys in which these rivers descend from the mountains, the ma- 
terials change with each successive ridge, the larger fragments being 
transported only short distances ; and that as the gravel advances into 
the plains, it becomes more finely comminuted ; Herefordshire and 
the low countries being chiefly covered with local debris of the old 
red sandstone. The author specially distinguishes this drift, which is 
extensively spread over valleys and slopes, and sometimes found in 
high situations, from the detritus which hasbeen carried down by rivers 
under the atmosphere, conceiving that the former accumulations have 
been washed down the surfaces of the inclined strata; because wherever 
the latter dip tothe S.E.,so are the materials invariably found to have 
been propelled in that direction. In no instance has any fragment 
been found on the west which can have been derived from rocks on 
the east. He therefore believes that at those periods when the Silu- 
rian and older rocks were raised from beneath the waters, great 
quantities of coarse and fine detritus were drifted down these slopes ; — 
and that as the rocks on which the loose materials have been depo- 
