160 J- T. Jutsonr 



places has a resemblance to an ordinary shallow artificial quarry 

 excavated in a similar locality. The slope of the hillside is usually 

 steep, or at a moderately high angle from the horizontal. Treat- 

 ing such slope as a plane, the outline of the quarry on such plane 

 would approximate towards a circle, and taking a section down the 

 slope through the quarry, the section line along the plane acrosa 

 the quarry would be the chord, and the outline of the quarry on 

 the section would be the arc, of a vertical circle. In some cases, 

 however, the lowest lip of the quarry may be removed by erosion, 

 and the quarry then passes gradually into the lower slope of the 

 hillside. 



The rocks of the hillside are either decomposed igneous rocks, 

 or normal sediments such as shales and grits. The igneous kinds- 

 predominate. The rocks must be soft and easily removed, and 

 therefore circular quarries are not found in the unweathered 

 granite and "greenstone." These soft rocks are frequently 

 capped by distinct bands of ironstone, or the surface layers of the 

 rocks may become indurated, without forming a distinct cap. The 

 upper surfaces, therefore, become resistant to erosion. The hard- 

 capped or surface-indiirated hills form lines of cliffs, known as 

 " breakaways," connecting a tableland with a lower plain. Small 

 water channels, which are usually mere furrows, one or two feet 

 wide and deep, may lead into the quarry at the top of it, or out of 

 it at its base. 



In surface dimensions the quarries range in diameter from a 

 few feet to perhaps 40 or 50 feet, and in depth from perhaps a 

 foot or two to five or six feet. They are generally shallow in pro- 

 portion to their surface area. 



The Eectanrjular Quarry. — This type is also found on hillsides. 

 Its floor, however, is practically coincident with the floor at the 

 base of, or with the floor of a bench on the hillside. It is different 

 from the circular quarry in that it is bounded by approximately 

 straight lines. Its " back " forms a steep usually vertical, or close 

 to the vertical, plane, Avhich intersects at an acute angle the plane 

 of the hillside. Its floor forms a plane but little inclined from the 

 horizontal, and practically coincident with and forming an exten- 

 sion of the floor at the base of, or of the floor of a bench on the hill- 

 side. Thus there is frequently but not always no "front" wall 

 dividing, or partly dividing, the quarry from the adjacent 

 floor; and where a wall does occur it is generally very low 

 and is always broken to allow for tlie passage of water from t he quarry. 



