MICHIGAN ACADEMY OF SCIENCE. 
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Australian coast to tlie Solomon Islands are attributable to pressure 
from that continent instead of toward it. As to the mid -Pacific ridges he 
is in doubt but leans toward a southwesterly, that is an Australian, 
source for the corrugating- pressure. That would restrict us to the space 
between Labrador and the mid-Pacific islands. Now. since the central 
portion of North America is known to have remained free from major 
deformation through Mesozoic and Tertiary time, the Pacific border of 
this continent is about all there is left to fall back upon. Let us see 
what measure of crustal shortening may reasonably be assigned to that 
region. 
The amount of crustal shortening in the Laramide range of the 
Canadian northwest was given by McConnell in 1887 as 25 miles in 50. 
That is, 50 miles of surface had been gathered into 25. This includes a 
thrust of Cambrian over Cretaceous of about 7 miles. Taking this into 
consideration, Dana, 1896, assigns to the Pacific border of North, “Lara- 
mide and other systems later than the Arcluean, not over 75 miles.” 
In the Appalachians, Claypole, 1885, found 153 miles (in Pennsyl- 
vania) shortened to 65, a difference of 88 miles. 
Willis, 1893, in Tennessee, found 72 miles shortened to 54, difference 
18, which measure lie considers “accordant" with Claypole’s results in 
Pennsylvania. 
For the Alps, Heim, 1874, found 74 miles of shortening, about the 
same as that given for our Pacific border. 
In regard to overtlirusts more particularly, although many are in- 
cluded in the above measurements, a few examples may serve to ac- 
quaint us with the general run of values; such are, one in the Laramide 
range (McConnell) 7 miles; one in Utah, 4 miles and more (Black- 
welder) ; in Montana one of 5 to 7 miles (Willis); Georgia, 11 miles 
(Hayes); in Scotland, one of 10 miles (Peach); numerous small ones 
in Europe and one in Scandinavia of 62 1 ,4 miles (Suess). The last is 
exceptionally large. Overthrusts are abundant in various regions but 
they are generally small. 
To be liberal with the theory, let us grant that there is much more 
shortening hidden in the Pacific border of North America than has hith- 
erto been supposed. Let us say that we will concede for that one region, 
in addition to Dana’s allowance of 75 miles, Olaypole's 88 for the Ap- 
palachians and Heim's 74 for the Alps. We secure a total of 237 miles, 
which is a fraction over 42% of the 560 miles of crustal creep of North 
America which we have to account for. More than half, 323 miles, is 
still missing, so to take care of that we have still to introduce somewhere 
between Labrador and the Solomon Islands the shortening equivalent 
of four such mountain regions as the average, (79 miles) of the Alps, 
Appalachians, and Pacific Border of North America. Recourse must 
doubtless be had to enormous theoretical thrusts, of the existence of 
which we have no knowledge whatsoever. 1 have selected this particular 
case, because it seems more favorable to the theory than any other. 
Between the Labrador coast and the Solomon Islands, we have some- 
thing like 9000 miles in which to find 560 miles of crustal puckering. 
We do not find it. 
If we take the case of western Eurasia, we have not over 2500 miles 
in which to take care of over 1000 miles of crustal creep. Reference to 
Mr. Taylor's figure 7 shows how few mountain ranges there are between 
