THE MECHANICAL INTERPRETATION OF JOINTS 23 
squeeze the dipping beds up from underneath the joint plane, out 
into the channel. 
Sections A and B (Fig. 19) show the result which is brought 
about entirely by a horizontal flowage of the beds beneath the 
joint plane in a direction perpendicular to the plane of the paper, 
and not to any horizontal compressive stresses acting within the 
plane of the paper. 
The joint nature of these ‘“‘fault” planes is brought out beauti- 
fully by the exposure shown in Figure 17, which for years has been 
well exposed in Westfork Creek at Cincinnati, just above the 
schoolhouse. 
There can be little doubt that essentially the same interpretation 
applies to other similar occurrences.* 
VI. HORIZONTAL COMPRESSIVE STRAINS IN GRANITE 
Compressive strains of considerable magnitude, essentially in a 
horizontal direction, exist at widely separated localities in all states 
of New England, if not throughout the whole region. In the 
quarries, the strains find expression in various ways. Vertical 
drill holes are flattened to an elliptical cross-section,? the cores 
between contiguous borings are crushed, and cracks open up 
diagonally from the channels. In the process of quarrying new 
fissures open up with a dull explosive noise,4 or new sheetlike 
partings form’ or old sheets buckle up.° 
With a detailed knowledge of most of the excellent exposures 
of sheeted granite in New England at his command, Dale has come 
to the conclusion that shrinkage in cooling, or changes of temper- 
ature, or other forms of weathering have played, at best, only a 
secondary réle in the production of the sheet structure; that the 
t A. H. Purdue, “Illustrated Note on a Miniature Overthrust Fault and Anticline,”’ 
Jour. Geol., Vol. TX (1901), pp. 341-42; C. E. Decker, unpublished manuscript, see 
Fig. 17, p. 39, Jour. Geol., Vol. XXVI (1918). 
2T. N. Dale, “The Granites of Vermont,” U.S. Geol. Survey, Bull. 404, p. 18, 
Fig. 2; Bull. 354, p. 34. 
3 [bid., Bull. 354, pp. 96 and 126; Bull. 313, pp. 12 and 142. 
4Tbid., Bull. 313, pp. 34 and 142. 
5 [bid., Bull. 404, pp. 97 and 107. 6 Ibid., Bull. 313, Pl. VII, A. 
