EEEL, Howorth—A Great Post-Glacial Flood. 361 
a considerable amount of time and trouble must be expended 
before anything from the Chalk would turn up. The district to 
which I refer is that comprising the south of Derry and Antrim, 
great part of Tyrone, and the northern part of Armagh. In those 
places I have examined many eravel-pits, and always noticed the 
distinction noticed above.” Mr. Hardman then goes on to argue 
that if the contents of the gravels had been derived from the Till, 
““we should expect to find in the re-arranged part the same con- 
stituents as in the so-called Till; or, to put it more clearly, all the 
pebbles of the gravels must previously have existed in the moraine 
matter of the glacier, and would be found in all parts of the Drift 
in nearly the same relative proportions. Were the proportion of 
chalk, etc., in the Till very variable, it might be supposed that 
these gravels had their origin in some such chalky Drift. But this 
is not consistent with the facts. The Till is remarkably free from 
such pebbles, and in the extensive district I have examined hardly 
any difference in this respect could be observed.” 
This is assuredly very important evidence. Jt is more than con- 
firmed when we turn from the pebbles to the sandy matrix in which 
they occur, and to the great beds of more or less clean sand that so 
often accompany the “eravel, and are intercalated with it. The 
texture and composition of these sands are so entirely different to 
those of the clays,\that it is impossible to assign them to the same 
origin. They are doubtless due to the trituration of entirely different 
rocks, the granular quartzose sands and the pulverulent argillaceous 
Till being obviously derived from a different matrix, and it being 
impossible to wash the one out of the other. Having decided this, 
we may next inquire whether the two sets of beds were distributed 
at virtually the same time and by the same forces, or whether there 
‘was a break and a hiatus between them. In studying the older 
rocks we should probably test such a question by the conformability 
or unconformability of the two. This is a very easy test in the case 
of rocks, but becomes difficult, and we have to rely on exceptional 
instances, in the case of the loose deposits, many of which are un- 
stratified or stratified most irregularly. Although there is no uncon- 
formability between the Boulder-clay and the overlying gravel in the 
ordinary sense of the word, there is what is equivalent to it, a proof 
in some places that between the two there was no continuity. Thus, 
to quote Mr. Geikie, who is arguing for quite a different purpose: “ At 
the top of the Cromer cliffs appear here and there considerable masses 
of sand and rolled gravel with marine shells. Mr. Wood has pointed 
out that these deposits rest upon a highly eroded surface of the con- 
torted drift, an appearance which was very noticeable when I visited 
ihe sections.” —“ Great Ice Age,” p. 546. Again, speaking of the 
sand and rolled gravel, etc., he says, ‘‘As these deposits rest often 
in hollows eroded in the till and underlying beds, it follows that 
a period of considerable denudation must have preceded their 
deposition. It is quite possible that a land surface may have existed 
prior to the formation of the ‘sand and rolled gravel,’ and much of 
the sand and gravel, which is for the most part fossiliferous, may be 
-of torrential or fluviatile origin” (4b. p. 391). 
