Dr. CO. Ricketts—Changes in the Earth’s Crust. 167 
Whernside, Ingleborough and Penigent, by the Yoredales and Mill- 
stone Grit. These also were formerly covered by a considerable 
thickness of Coal-measures, as is evident from the presence of the 
Coal-field of Ingleton on the southern or down-throw side of the 
Great Craven Fault; whilst the whole series rested in a position as 
horizontal as when first laid down, though, in order to permit the 
accumulation of this succession of strata, they must have sunk con- 
tinuously whilst deposition progressed, until their base reached a 
depth of 4500 feet, as calculated by Professor John Phillips. 
The difference in the conditions of the two series is remarkable ; 
for if the foldings in the more ancient strata are attributable to 
lateral pressure, due to subsidence, they should have occurred also, at 
least to some extent, in the Carboniferous rocks in which subsidence 
took place to the depth of nearly a mile. It is therefore necessary 
to search for other causes likely to effect this pressure. 
Sir Charles Lyell, when commenting on the presence of the “mud 
lumps” at one or other of the mouths of the Mississippi, attributed 
their formation to ‘the downward pressure of the gravel, sand and 
sediment, accumulated during the flood season off the various mouths 
of the river, upon a yielding bottom of fine mud and sand. A mass of 
such enormous volume and weight, thrown down on a foundation of 
yielding mud, may well be conceived to exert a downward pressure, 
capable of squeezing and forcing up laterally some parts of the 
adjoining bottom of the gulf, so as to give rise to new shoals and 
islands.” He further states “that railway engineers are familiar 
with the swelling of a peat moss, or the bed of a morass, on some 
adjoining part of which a new embankment has been constructed.? 
A friend who, many years ago, was engaged in superintending the 
erection of a fort near the mouth of the Medway, relates that the 
unloading of a cargo of materials to be used in its construction 
caused a considerable deviation from the perpendicular, and great 
difficulty was likewise experienced in keeping the structure erect as 
it progressed, on account of the muddy deposit, on which the founda- 
tions rested, giving way irregularly. 
Captain CO. KE. Dutton, of U.S. Geological Survey, states that 
‘“‘wherever the load of sediment becomes heaviest, there they sink 
deepest, protruding the colloid magma beneath them to the adjoining 
areas which are less heavily weighted, forming at once both syn- 
clinals and anticlinals.” * 
Though Lyell, as has been already remarked, considered that the 
intense pressure by which foldings of strata have been caused, has 
been exerted without violence, and in the most gradual manner, he 
omitted to apply the phenomena, described by him as occurring at 
the mouth of the Mississippi, in explanation of the cause of contortions 
in older rocks. 
1 Report on the Probability of the Occurrence of Coal in the Vicinity of Lancaster, 
37 
o Principles of Geology, 10th edit. vol. i. p. 453. 
5 The Karth’s Physical Evolution, The Penn Monthly, 1876, p. 424; also a 
resumé of the same, by Rey. O. Fisher, Grou, Maga. Dec. II. Vol. III. p. 374. 
