Dr. Irving—Surface- Changes in London Basin. 213 
under the term “glacial gravels” we include (as I have done all 
along) those gravelly deposits whose actual structure seems to 
record the operation of ice as the chief agency, to which the observed 
structural phenomena are due, we must, as a matter of fact, include 
in the glacial category many deposits, which might perhaps be 
excluded therefrom, if we used the term ‘“ Glacial” (always mind 
with a “G”’) in the narrower and professional sense of the car- 
tographer, which seems to include only those deposits which contain 
materials foreign to the area in question, such, for example, as the 
quartzite pebbles derived from the Trias of the Midlands. It is, I 
imagine, in this narrow and technical sense of the term “ Glacial,” 
that the author of the paper referred to at the beginning of this 
article is inclined to dispute the admission into the glacial series of 
the contorted gravels and clays at Ninemile Ride, Berks, of which 
photographs have been taken for the British Association, two of 
which have been published (one in “ Proc. Geol. Assoc,” the other 
in “Science Gossip”), which, moreover, carried the strongest evidence 
of glacial action, not only to my mind, but to that also of Prof. 
Spencer, the State Geologist of Georgia (a well-known writer on 
glaciation), when I took him to the sections in 1890. 
Similar contortions and puckering of the well-banded clay (No. 5 
of the College well-section) are exposed to view in the deep trench 
by the birch-avenue leading from the Station to the College, which 
was dug two winters ago. Considerable masses of gravel (chiefly the 
wreckage of the pebble-bed) are here also driven down into the clay. 
I would remind the reader, that, when it comes to the considera- 
tion of a case in which glacial action is involved, the value of in- 
dividual judgments is to a great extent determined by the knowledge 
on the part of those who form such judgments, (1) of the actual 
physical laws concerned in the question under consideration, (2) of 
the phenomena usually known as “glacial” from personal obser- 
-vation of known glaciated regions, such as those of the Alps and other 
mountain districts. Were it not that I believe him to have been 
caught in the technical fallacy indicated above, in his forced and 
artificially-restricted use of the term “glacial” on pp. 40-41 of his 
paper, I should consider Mr. Monckton’s idea too preposterous to 
admit of serious discussion. . 
But the same writer has a way of criticising such caricatures of 
the ideas or theories or views of another writer, as are creatures 
of. his own imagination. So, without really understanding the 
theory of the late Prof. Carvill Lewis, of Philadelphia, as to the 
glaciation of the Mercian and Hast-Anglian regions, and the relation 
of that to the glaciation of the Thames Valley, he falls into the 
mistake of supposing that it requires us to “argue for the presence 
of the sea in this part of the Thames Valley in Glacial times”; while 
in reality I have but applied the term “Thames Straits” (as writers 
before me have spoken of the “Severn Straits”) to the broad expanse 
of water, down which probably ice-floes from the Mercian region 
floated, through the higher part of the Goring-Pangbourne Gorge, 
which has undoubtedly been much deepened and widened beth 
