THE WORK OF WATERS UNDERGROUND 117 



greatly when it contains carbon, dioxide dissolved from the 

 air, and to some extent when it contains matter derived 

 from decaying vegetation. z - 

 Since temperature and pressure aE 

 increase with depth, it might 

 at first thought appear that 

 solution by ground waters 

 should be most important near 

 the base of the zone of frac- 

 ture. It is evident, however, 

 that for the continuation of 

 this work there must be active 

 circulation of the water ; water FlG -. 109 ; ~ Pr fi le of Turtle Moun " 



tam, Alberta, showing the amount 



charged with mineral matter 

 in solution must be withdrawn 

 to make room for other water 

 able to dissolve more. As in- 

 dicated on page 80, the zone of 

 greatest solution is accordingly 

 near the surface, where circula- 

 tion is most active. Below this the dominant thing is deposi- 

 tion, rather than solution. It is, of course, not to be inferred 

 that no solution occurs in the lower zone of deposition, or 

 that deposition does not occur in the zone of solution. 



Rocks are made porous and weakened by the withdrawal 

 in solution of their soluble constituents, and solution is one 

 of the most important processes in the weathering of rocks. 

 Thus, if its cement be removed in solution, sandstone crumbles 

 into sand, and conglomerate into gravel. Carbonated ground 

 water (water containing carbon dioxide) sometimes removes 

 so much limestone in solution from a given place that a 

 cave or cavern is formed (Fig. 110). Such caves are com- 

 mon in parts of Kentucky and Indiana. There are said 

 to be over 100,000 miles of underground chambers in 

 the limestone rocks of the former state. The thinned and 

 weakened roofs of caverns may fall in, forming surface 



B. & B. GEOL. 8 



of material removed in the Frank 

 landslide of Apr. 29, 1903. A mass 

 of rock nearly half a mile square 

 and some 400 to 500 feet thick in 

 places broke suddenly from the 

 east face of the mountain and de- 

 scended with great violence to the 

 valley below, destroying part of the 

 town of Frank. 



