[HILL-ToUr] PREHISTORIC MAN IN BRITISH COLUMBIA 105 
eause of the abandonment of so ancient a camping-ground may possibly 
be found in this last reason. That is a gradual, or possibly a sudden, 
deposition of river detritus on these flats raised them above the reach of 
ordinary tides. and so brought about the extinction of the shell-fish at this 
point, and made it desirable for the natives to seek a camp lower down 
the river, where the molluscs were able, as now, to maintain an existence. 
This explanation has the advantage of simplicity, and seems plausible ; 
but the former cause suggested is not unlikely the truer one. The aban- 
donment, many centuries ago, of so many other middens elsewhere in the 
district along the neighbouring bays and inlets, where no such cause as this 
ean be assigned—where clams and mussels still exist in great quantities, 
and have so existed from time immemorial, as the extensive midden-piles 
now testify—seems to call for a more comprehensive and less local explan- 
ation. And further evidence and a more thorough investigation than I 
have thus far been able to give them may confirm the conjecture, which 
certain other evidence would seem to support, that the intrusion of the 
Salishan emigrants into this district, and the inevitable extermination of 
many of the former inhabitants, is more likely the real cause of the deser- 
tion of this and the many other ancient camping-grounds of this region. 
Should this conjecture hereafter prove to be the truth, the results of 
Dr. Boas’s study of the Cowitchin tongue will receive an interesting and 
independent confirmation. The discussion and settlement of this ques- 
tion, however, must needs be left till further evidence has been gathered, 
In considering the time when the abandonment took place, the phys- 
ical changes which have clearly taken place in the estuary since the 
shells which enter so largely into the composition of the middens were 
gathered from the tidal-flats that have since become tree-clad and cul- 
tivable islands, afford us some clue to work upon in the case of the mid- 
den under consideration. If we can arrive at an estimate of the age of 
the islands, we shall get some idea of the period of abandonment ; for 
there is little doubt, I think, that these Fraser middens were wholly formed 
before those physical changes which transformed the shell-bearing flats 
into islands, took place. In seeking to form this estimate, we are assisted 
in some measure by the independent, extraneous evidence of the enormous 
tree-stumps now found in the midden; and although Professor Cyrus 
Thomas has shown, in his investigations among the mounds east of the 
Rockies, that no great reliance can be placed upon the evidence of the age 
of trees based upon the number of their rings, the size, condition and other 
characteristics of these stumps, all warrant one in saying that many of 
them are from 500 to 700 years old. The age of the islands, then, cannot 
be less than the age of the midden trees, though it may not be very con- 
siderably greater. Exactly how much older they are it seems impossible, 
from the evidence at hand at present, to say with any certainty. There 
is nothing in their formation, as far as I have been able to learn, for 
