164 J. T. Jutson : "Natural Quarries." 



above, either of these two rock arrangements necessarily tending- 

 to produce a steep cliff. It is possible also that water finds its way 

 down through the rocks and oozes out at the base of the cliff; and 

 so may slightly remove, or at any rate weaken the soft rocks at the- 

 base of the cliff. When these (quarries occur at the edge of " dry " 

 lakes bounded by rocky cliffs, the crystallization of salt from water 

 evaporating from the rocks at the base of the cliffs may also help- 

 this type of quarry formation, l)ut further investigation is desir- 

 able on this point. 



The triangular quarries are due to the gouging action of rain on 

 soft rocks. Their form is guided by the hard rocks forming a cap- 

 to the " back," which cap resists erosion and brings about the 

 steep "back." At the same time the check given to erosion by 

 such cap causes the denuding agents to follow the line of least 

 resistance, with the result that the quarry is widened between the 

 sides of the triangle, thus causing a lengthening of the "back" 

 along the base of the triangle. 



EXPLANATION OF PLATES. 

 Plate XXVIII. 

 Fig. A. — Section through a circular quarry. Tlie broken lines- 

 indicate the original surface, which has now been removed. 



Fig. B. — Block diagram illustrating the formation of a triangular 

 quarry with a hard cap to the " back." 



Figs. C. and D. — Sections illustrating the formation of rect- 

 angular quarries, the broken lines being the original surfaces, now 

 removed. 



Platr XXIX. 



Fig. E. — A circular quarry, Niagara. 



Fig. F. — A rectangular quarry, western shore of Lake Goongarrie^ 

 Comet Vale. 



