118 



SCIENCE. 



[N. S. Vol. IL No. 31. 



is nothing more nor less than a crack in 

 the rock. The plateau is there constituted 

 of limestone, the Aubrey limestone of the 

 Carboniferous system. The rock is trav- 



the limestone yields less readily to erosive 

 agents than the soft overlying shale. The 

 crack referred to traverses one of the lime- 

 stone blocks for a distance of 800 or 1000 



ersed by great faults and flexures, chiefly of feet, and ends abruptly against a fault, as 



Fig. 1. View of rock fissure, clxawn from photograph. 



middle Tertiary date, and since these were 

 formed the region has been extensively de- 

 degi-aded. In the immediate vicinity of the 

 ranch are several small faults, from 10 to 50 

 feet in throw, and these are clearly ex- 

 pressed in the topogi-aphy, not, I think, be- 

 cause they are freshly formed, but because 



indicated diagrammatically in figure 2. 

 It is there 6 or 8 feet wide, and it tapers 

 gradually to the other end. In the down- 

 ward direction it is said to taper also, the 

 width diminishing from 4 or 5 feet to about 

 one foot in 100 feet of descent, at the point 

 where water is drawn. The water, which 



