168 Dr. C. Ricketts— Changes in the Earth's Crust. 
It is deserving of consideration whether, and to what extent, fold- 
ings of strata, and other concomitant phenomena, have been depen- 
dent on varying accumulations of material. A river brings down and 
deposits a greater quantity and coarser particles, in an estuary or 
bay, or in the sea, along the direction of its current, than at a 
distance, where the finer mud is spread out; when this occurs above 
an underlying muddy deposit, there would be a tendency for the 
heavier materials to sink down and, producing displacement, so cause 
lateral pressure similar to that to which these foldings have been 
) 
: 
, ML hii cco! mma 
if} 
] / 
il i 
} Hf} / My y Mi Y 
A THM MMM 
Yih Mii} 
ee d Yip y Wy pp 
Mary 4 Ly L 
L 
li L Tl l 
z 
| LT ATT ATMO g 
y Ip i 
| ] ao 
Fig. 4. C, consolidated Clay ; B, layers of Clay, originally in horizontal beds, but 
squeezed into folds by the vertical pressure of S, sand, extra weight being applied. 
attributed since the days of Sir James Hall. Effects correspondmg 
to these suppositions can be readily induced by taking clay dried 
and reduced to powder and spread in consecutive layers of different 
colours horizontally in a box or trough. On the access of water, 
through holes previously made in the bottom and sides of the box 
rather than by pouring it on the surface (for that would prevent the 
free escape of the included air) the clay becomes soft and plastic ; 
when fully saturated, by pouring sand on the clay at some special 
part and applying extra weight, which will be requisite in the 
experiment, this will not only cause the heavier substance to subside 
into the plastic mass of clay, but, whilst pressing downward, it will 
at the same time squeeze outward the clay-beds, causing the layers 
immediately underneath to be formed into films; these, however 
thin, are still continuous with those on the sides, which are rendered 
considerably thicker than in the original state of the beds, and are 
curved into folds, representing contortions similar to what are con- 
stantly met with, having been produced under circumstances analo- 
gous to what must frequently occur from natural causes (see Fig. 4). 
That the form of the contortions may be greatly influenced by the 
contour of the solid ground is well illustrated in the effects produced 
by the presence of the mound (*) of consolidated clay (C) in the 
figured model. (The interior of the models was displayed by cutting 
through them, before they became solid, by means of a piece of 
string, previously arranged for that purpose.) 
From the great thickness of certain geological strata, from the 
amount of deposit known by borings to occur in the Deltas of great 
