190 The American Geologist. March isqo 
The nonsensical theory appeared over Mr.'Cresson's name, and stood 
for two years and three months. Perhaps your readers can reconcile 
these statements. The pile dwellings are evidently fish-weirs. They 
may have been made by Indians and they may not. The reliability of 
the person describing them is exceedingly doubtful. 
Eespectfully yours, 
Mendon, Ills., Feb. 19, 1S90. Stephen D. Peet. 
The Level op no Strain. — Students of geology must thank professor 
Claypole for' his simple presentation of the question now so actively 
discussed by certain English physical geologists regarding the "Level 
of no Strain" within the earth. Teachers should also be interested in 
it, for if the discussion lead to a valid conclusion, the Contractional 
Hypothesis that is so generally tauglit to their classes, ought to be 
abandoned, except in teaching the historj^'of geology. But is not their 
conclusion — namely, that the depth of the level of no strain is only ten 
or twelve miles below the surface — only a special solution of the prob- 
lem of a cooling body? It rests, as professor Claypole shows clearly, 
on the absence of cooling below a depth of 400 miles, and this in turn 
rests on the postulate that the temperature of the earth was once uni- 
form from suiface to center. Why should a highly specialized initial 
distribution of internal temperature be accepted as the only one 
worthy of discussion? I have sometimes wondered if it were not chos- 
en on account of its simplicity ; but certainly there are other conceiv- 
able and admissable initial distributions that deserve consideration. 
The uniform distribution of temperature rests on the supposition of 
convectional movements by which all previous inequalities of temper- 
ature were equalized. It is very questionable whether such movement 
could continue until anything like equality of temperature was attained ; 
viscosity and friction would exceed the relatively small gravitative 
forces, on which the latter stages of convection must depend, long 
before equality of temperature within and without was reached. 
Moreover, an essential of the postulate of uniform initial distribution 
of temperature is a sub-postulate of uniform distribution of specific 
gravities, and this is altogether unlikely. The whole contractional 
hypothesis, with its various postulates, rests in turn on the nebular 
hypothesis, in which there is nothing to forbid and everything to sug- 
gest that the nuclei of the planetary masses were denser than the 
subsequent external accretions ; and if we postulate such an origin for 
the mass of the earth the possibility of the convectional equalization 
of central and superficial temperature is entirely excluded. An enor- 
mou'^ exce-^s of temperature might remain about the center without 
causing suflScient expansion of the dense material there to produce 
convectional unstability. A crust would form and geological opera- 
tions would proceed in their recognized order while a vast store of 
heat remained imprisoned within ; and the level of no str^iin at the 
present stage of the history of such an earth, would be much deeper 
