Correspondence—Mr. J. Rk. Dakyns—H. B. W. 93 
better preservation of Jake-basins in glaciated countries from silting up 
and from becoming thus obliterated, while in some glaciated regions 
lakes are wanting. 
CORR mS 2 @ ina zaaN Ca 
Be igs a 
THE BRIDLINGTON CRAG. 
Str,—There seems to be some misapprehension about the 
Bridlington Crag. 
In the Geological Record for 1878, on page 38, there occurs the 
following passage: “ Confirms the succession given by Mr. Lamplugh 
that the ‘Crag’ bed lies on the blue clay or basement bed, but is 
below the snuff-coloured laminated clay, while the purple clay 
is above the last.” 
Now Mr. Lamplugh has conclusively shown that the Bridlington 
Crag is not a bed at all, but a series of patches, boulders in fact, 
included in the so-called Basement Clay. 
The bed or beds whence the shells were originally derived, if still 
existing, has never yet been seen. I say ‘“‘or beds” because shells 
that lived at different depths have been brought together at Brid- 
lington. _ J.B. Daxkyns. 
MELMERBY, PENRITH. 
DR. RICKETTS.—ON SUBSIDENCE AND ACCUMULATION. 
Str,—In connexion with the subject of Mr. Jamieson’s paper on 
the Cause of the Depression and Re-elevation of the Land during 
the Glacial Period (Gnon. Mac. Sept. and Oct. 1882), it may be 
interesting to re-direct attention to a paper by Dr. Charles Ricketts, 
On Subsidence as the Effect of Accumulation (Grou. Mace. Dec. I. 
Vol. IX. p. 119); and to his presidential address to the Liverpool 
Geological Society in 1872, on Valleys, Deltas, Bays, and Estuaries. 
He has, in the latter paper, expressed his opinion that during the 
Glacial period the combined weight of ice and boulder-clay would 
produce subsidence of the land; and again, in speaking of deltas, he 
concluded that the steady accumulation of mud would in the end 
cause subsidence, gradual and imperceptible at first, but under 
certain conditions perhaps sudden. 
The observations of Messrs. G. and H. Darwin, noticed in a late 
number of the GronogicaL Macazine, by Prof. Milne, show that 
the crust of our earth is more susceptible than we imagined when, 
ten years ago (Gro. Maa. Vol. X. pp. 88 and 141), we ventured to 
criticize somewhat unfavourably the views then put forward by Dr. 
Ricketts. H. B. W. 
TERRACES IN DORSET. 
Srr,—There are to be seen on the sides of the valleys in Dorset 
a number of terraces, which are, I believe, a peculiar geological 
feature of that and a neighbouring county. I have never yet seen 
a satisfactory theory as to their origin. It has been asserted that 
they are old fortifications ; also that they have been formed by the 
plough. Whether the sea-beach or lake-beach theory has ever been 
