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30 or 50 yards wide, and 15 feet deep, have been filled up to the extent 
of six feet in a single year ; and you will find frequently six feet of level 
deposit laid in one of those channels in a single season, and sometimes six 
inches will be laid in one set of spring tides, which I think are generally 
reckoned to number three, or four, or five. Seeing, then, that deposits 
depend on the continuity or interruption of a stream, there can be no law of 
deposits, especially when the flow of that stream often depends on accidental 
circumstances. (Hear, hear.) There is another fact supplied by this district 
which affects the question of coast elevation. This very district of which I 
have been speaking, extending over about 20,000 acres, has not been 
elevated, but depressed. It was, in fact, once a forest, and the farmers dig 
up the trees in situ , split them, and carry them into the market towns 
for kindlings [firewood]. If the sea was to be let in over that area it would 
cover it to a depth of six or eight feet. How, then, could the forest 
have grown there at the present level? And we know there have been 
no artificial embankments to keep the tide out, excepting those which have 
been very recently made. The country has been depressed, and altered its 
level ; and it is because of that depression that we can carry on the 
system of warping, and at the end of two years or so improve land 
worth ten shillings an acre till its value is fifty shillings an acre. There is 
thus a law of depression as well as a law of elevation, and in studying this 
question we should remember the operation of those laws. It is only 
by treating geology in this way — first the fact and then the inference — that 
you can arrive at anything like reliable results. If we take the inference 
without the fact we are sure to be wrong, and unquestionably we have of late 
been doing what is very like that. We have been too rapid in the formation 
of our theories ; we have reduced them to form and moulded a system, and 
now that facts are breaking in upon us they are completely destroying our 
system, and we have to begin our learning anew. (Applause.) We ought to 
be much obliged to Mr. Mitchell for his very able paper ; and I trust that 
we shall have other papers of that kind from time to time. 
Mr. Brooke, C.E. — I have been largely engaged for twenty-four years in 
the navigation of rivers, and I, too, can speak of the effects of currents upon 
deposits. A reference was made to the Nile. The International Committee 
report that in the borings for the Suez Canal marine shells were found of the 
same kind as those which now exist in the Bed Sea. The deposits of the 
Nile are sometimes spoken of as though they were only deposits of mud ; 
they are vast deposits of sand 
The Chairman. — Would you be good enough to state whether you are 
speaking of the bed of the river, or of the Delta ? 
Mr. Brooke. — If you wish to consider the deposit higher up above Cairo, 
you must remember the effect of damming up the stream. The works 
of recent pashas must of necessity have had their effects upon the deposits 
both above and below, and we know not but that similar works may 
have existed in times gone by. I repudiate the notion that we are called 
upon to believe the theories which Mr. Mitchell has so ably combated. 
