Petrographical Differentiation of certain dykes. 153 
in spite of its enormous strength it sank below water and was 
drowned. Decaying and perhaps in part devoured by other ani- 
mals its bones fell asunder and were scattered over the bottom of 
the lake as they have now been found. On this view others 
probably remain to be recovered, as the}' may lie at some distance 
from the spot first struck. So large a bone as the pelvis can 
scarcely have perished when the clavicle and claws remain perfect. 
The skull also should be found, and the lower jaw which is one of 
the most enduring of the bones and is frequently preserved when 
no other part of the skeleton remains. 
VII. Its date. 
In regard to the date that should be assigned to the creature it 
is evident that it is post glacial, and as we are unable to assign to 
the end of the ice-age in this state an antiquity of more than about 
10,000 years this puts an upper limit on the age of the fossil. 
Yet farther, as the cold had entirely passed away and the climate 
had become almost or quite as to-day, this date must be much 
farther reduced. And this reduction may be very considerable. 
We have no reason to doubt that the Megalonyx came into the 
region as soon as the climate was suitable both for itself and its 
vegetable food. And that it survived into the human period we 
have no reason to doubt. Though there is yet no evidence of man 
and Megalon3 T x in combination, yet there is reason for believing 
in the contemporaneity of man and other huge Mammalia in North 
America. Moreover, the occurrence of one specimen in Tennes- 
see yet retaining fragments of cartilage and tendon attached to its 
bones is another proof that the species lingered or survived till 
quite recent times. Whether the specimen in Holmes Co. then 
belongs to an ancient or a recent animal it is not possible to say, 
and all that can be determined is that its age probabl}* lies be- 
tween two and eight thousand years. 
PETROGRAPHICAL DIFFERENTIATION OF CER- 
TAIN DYKES OF THE RAINY LAKE REGION. 
By Andrew C. Lawson, with analyses by V. T. Sin tt, M. A., F. C. L 
< ommunlcal ion No. 2. 
At the Toronto meeting of the A. A. A. S. the writer- sub- 
mitted a paper in abstract bearing the above title. The materia] 
for the full paper was not at the time of the meeting complete, 
