262 



The Mount Lofty ridge is in a. condition of relatively 

 rapid waste. The felspathic quartzites, of ^vhich it is largely 

 composed, are greatly decomposed and but slightly cemented. 

 When the mechanical action of running water is brought to 

 bear on this material it is rapidly eroaed. The clearing of 

 scrub-lands and the cultivation of steep slopes are important 

 contributory factors in producing this result. As the inco- 

 herent material is carried away by rain and rivers, the sili- 

 ceous outcrops will become more prominent, and the valleys, 

 following the direction of the more friable material, will be- 

 come widened and deepened. In certain places this rapid 

 denudation may ha^^e a disastrous effect on the productiveness 

 of the gullies, and an economic foresight suggests that every 

 effort should be exercised to conserve the soil in such situ- 

 ations where, by baring and loosening the ground under cul- 

 tivation, it is liable to waste to an excessive degree. 



EXPLANATION OF PLATE XII. 



Fig. 1. Diagrammatic section of the Lower Cambrian beds 

 from the River Torrens to the sea — about 15 miles. 



Fig. 2. Diagrammatic section, from Mount Lofty to Aldgate, 

 t-o illustrate liow the Lower Limestone may be prevented from, 

 outci-opping at the surface. Two parallel trough faults are ehown 

 in the section, by which the beds are throAvn down to the east, 

 and thereby cut off the limestone. 



Fig. 3. Diagrammatic section, in which another explanation 

 for the absence of the limestone at the surface is given, as alter- 

 native to the fonner. The section shows a normal fault, which 

 hades in the direction of the dip of the bedp. By this move- 

 ment some beds slide doAvn the fault-plane, and are thereby cut 

 of} fiom the .surface. 



