288 TRANSACTIONS OF THE CANADIAN INSTITUTE. {[Vor. VIII. 
was ‘‘thirty years old and its actual growth had been watched by Nor- 
denskiold.”’ 
Perched blocks cannot be well accounted for by. any ice theory, 
as they are balanced on comparatively small bases, which preclude the 
possibility of their having been dropped or rolled. Generally they are 
found in the neighbourhood,or on the flanks of hills, where their presence 
can only be attributed to a débacle. Sharp points or ridges projecting 
from the general surface, would naturally arrest them as they were being 
violently swept along by the flood, and as the wave subsided, probably 
gently, it would leave them supported through the line of their centre 
of gravity, leaning against or perched upon these arresting projections. 
Sir James Hall describes a somewhat similar phenomenon known 
as crag and tail. ‘‘When an obstacle whose height is equal or greater 
than its breadth, stands in the way of a running stream, it generally 
causes a stagnation, on the side towards which the stream is flowing, a 
deposition is formed of the transported substances constituting a tail or 
prolongation, which extends in the direction of the stream, by a gradual _ 
descent to the distance frequently of eight or ten times the height of the 
obstacle, while a hollow or depression is frequently caused on the other 
side of the obstacle by the accelerated motion of the stream there.” If 
we examine the bed of any rocky mountain stream, we find the largest 
stones at the greatest altitude and we find them reducing in size as we 
descend the stream. We see it widening out and becoming more sluggish 
until ultimately it deposits nothing but sand and mud. Now, if we 
postulate a sudden potential diluvial wave, such as has been described by 
Murchison or such as have recently taken place at Samoa, denuding and 
carrying along with it, every obstacle that obstructs its passage, passing 
over hills and dales and tearing along the sides of the highest mountains, 
then gradually subsiding after having reached its maximum velocity, 
we should find the débris deposited by it, large and small stones irregu- 
larly mixed with sand and clay without any general stratification. We 
should expect to find the crag and tail phenomenon, also asar or whale 
back ridges, just as we find till or boulder clay heterogeneously mixed 
(that has sometimes been mistaken for moraines). We would also find 
boulders of various sizes (the largest stopping first) rounded, scattered - 
and fanwise, in fact a reduplication of erratics. We would also find 
strie marks caused by the rapid passage of these boulders, stone and sand 
not only upon the rocks which have been passed over, but upon the boulders 
and stones themselves and we would find these strize marks sometimes in 
straight continuous lines, sometimes slightly deflected by opposing ob- 
stacles, which also results in cross hatching, where boulders have been 
diverted by impact, or some other cause, across the current of the débacle. 
gS «Shon heer 
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