359 
PROFESSOR HUGHES’ REPLY TO THE FOREGOING 
COMMUNICATIONS. 
It gives me great satisfaction to meet with the approval of so skilled and 
careful an observer as the Duke of Argyll, and I quite agree with his Grace 
in believing that, whether we are investigating the evidence for the antiquity 
of man, or the sequence of events which we include in what is known as the 
Glacial period, the most important inquiry is, — what was the extent, horizontal 
and vertical, of the last great movement of depression in the British Isles ? 
It marks the close of our Glacial period, and seems to precede the commence- 
ment of our human period. It was probably the sea of that submergence 
that lifted off the last of the ice. We do not expect to find traces of man’s 
sojourn here when the whole was covered by ice, nor was he likely to have 
left much indication of his visits when the greater part was covered by water. 
I did not go into this question, because I have not within my own know- 
ledge any evidence of remains of man having been found in the marine 
deposits of that age. 
With regard to Prof. Birks’ observations, I may remark that, as I cannot 
regard the astronomical combinations referred to as even the principal cause 
of the prevalence of Alpine conditions in our area at any period, I, of course, 
cannot accept them as a measure of the age of the Glacial period. I think, 
on referring to my paper, it will be seen that I do not lay much stress on the 
contemporaneousness of man with certain extinct mammals, except so far as 
we can infer that such palaeontological changes seem to take place slowly, 
and to be dependent on terrestrial movements, which also, we believe, take 
place gradually. To the growth of stalagmite as a measure of time I attach 
no importance, and have made full allowance for local changes of level, which 
would accelerate the rate of waste. I appeal to river terraces, not to any 
doubtful deposits which may be due to cataclysmic action. What it comes 
to is this, — that there is at present no certainty about the age of the old river- 
terraces in which we find the remains of man ; but apply what test we will, 
we have always the same result, that, according to observed rates of change, 
the time must have been very long, unless we assume that every case that 
has been examined is an exceptional one, in which there has been an excep- 
tional and local acceleration of all the operations of nature. 
I must ask ^Ir. Brass to read the former paper by myself, referred to in 
p. 10, and I think he will see that I am far from assuming that no recent 
changes of level have taken place affecting the flow of rivers and the rate of 
waste in valleys. It is the recognition of this and other similar facts that 
makes me believe that in the present state of our knowledge it is impossible 
to assign a term of years to the period during which the rivers have been 
at work. 
Whether a valley has been in the main cut out by an ordinary river or by 
