24 WALTER H. BUCHER 
main factor has been horizontal compressive stress such as now 
finds expression in the region." 
This is not the place nor the time to enter into-a discussion of 
this complex problem. ‘The final word has not yet been spoken. 
If we assume, for the time being, a diastrophic origin of the 
observed strains, we can point to three observations favoring such 
a view. 
t. For at least one locality, the famous Quincy quarries south 
of Boston, Dale records the observation that “‘this strain in some 
quarries appears to increase with their depth.’” 
2. At Fletcher Quarry, on Robeson Mountain, in Washington 
County, Vermont, Dale observed what he called ‘‘double-sheet” 
structure. Here, instead of the usual single set of sheets, two 
such sets, intersecting at an angle of about 42° are exposed. If 
we analyze their position according to the method described in the 
first part of this paper we find that the bisectrix of the acute angle, 
that is, the direction of the greatest principal (compressive) stress, 
trends N. 60 W.-S. 60 E. and that it differs but slightly from the 
horizontal, being slightly directed downward toward the southeast. 
The least (tensile) principal stress, on the other hand, is practically 
directed upward, in the direction of easiest relief from the horizontal 
pressure. 
Fortunately, there is, at the same locality, ““a marked north- 
east-southwest compressive strain in the upper part of the quarry, 
raising the sheets and even forming new sheet partings.” The 
direction of this strain is essentially that which would result from 
the compressive stress, acting from the northwest, inferred from 
the ‘“double-sheets.” While this may, of course, be a mere coin- 
cidence, it certainly is suggestive of a causal connection. 
None of the other quite numerous cases in which Dale records 
the direction of compressive strain, together with data concerning 
the position of the sheet structure, can be used to test this matter 
«T. N. Dale, ‘The Granites of Connecticut,” U.S. Geol. Survey, Bull. 484 (1911), 
Pp. 29-36. 
2 U.S. Geol. Survey, Bull. 354, p. 96. 
3 If we had reason to believe that the granite had been in a ductile state when 
these planes of parting were formed, the stresses would have to be reversed. Butall 
observations seem to speak against this possibility. 
