Correspondence—Mr. Frank Rutley. 239 
to be owing to the sharp folding of the chalk, causing irregular 
cavities to open in various places, these cavities being subsequently 
either filled with material from above, which would naturally be 
stratified, as is often the case with cave deposits, or, as in one instance 
that I examined, apparently always empty. The folding of the 
chalk shown in my woodcut can now be easily examined; but in 1868, 
as shown by Mr. Fisher, the beach was much higher. 
The diagram, Fig. 4, of my paper, was only intended to give a 
general idea of my theory: of course in practice soft beds would 
take much more complicated folds, though their general direction is 
still distinctly traceable. Unfortunately, there are only short sections 
to be seen at right angles to the folds. 
The extreme shallowness of the North Sea is such that ice even 
250 feet thick would be more than sufficient to dam out all the 
water in the southern part, and supposing a submergence of 200 feet 
at the time of the Chalky Boulder-clay, about 500 feet of ice would 
do the same. At the same time the beds immediately below hoth 
the Till and the Chalky Boulder-clay are fresh-water and not marine. 
Nowhere in the south or east of England have I been able to obtain 
evidence of a contemporaneous marine fauna in any Boulder-clay. 
With regard to the so-called “Great Submergence,” Hast Anglia has 
at present yielded no trace of it; and if it had affected this district, 
one would naturally expect to find remains of deep-water deposits in 
such a flat country. Crement Rep. 
THE TERM ‘“SCHIST.”’ 
Srr,—The question raised by Dr. Callaway in the last number of 
the GrontocicaL Macazine will doubtless elicit many answers 
embodying various shades of opinion. Be these opinions what they 
may, the word Schist has in one respect a definite signification in 
common with the word schism. 
A schism is a split of some kind, it may be large or small. A 
fault is a schism; a joint-plane is a schism; cleavage is schismatic, 
and foliation and lamination also give rise to schismatic or schistose 
tendencies in the rocks in which they occur. I think, therefore, 
that Mr. Allport is perfectly justified in using the adjectives schistose 
and fissile synonymously. 
The only restriction which long usage appears to have imposed 
upon the term “‘schist” is that, whether a foliated or a laminated 
rock, the planes of fission (if planes they can be called, for they are 
often small and irregular surfaces of parting) should coincide either 
with the direction of lamination or with that of foliation. Foliation 
and lamination are not always coincident. 
It seems no reason that because the chief foliated rocks are spoken 
of as “crystalline schists ” that therefore, no other rock, no matter 
how fissile, should be excluded from the benefit of a term to which 
its structure may quite well entitle it. 
To express my own opinion, I should say that I fail to appreciate 
Jukes’s definition, and that in common with Mr. Allport I use schis- 
tose and fissile as convertible terms when the fission is not of that 
