136 



TRANSACTIONS 



i899-'oo 



without too much difficulty, since a little observation of regions 

 quite accessible to us, shows us very marked traces of" the period 

 itself. Of course the influence of new forces comes into play on 

 what is now dry land. Atmospheric effects, vegetable and 

 animal life, sunshine and storm play their part in altering the 

 surface ; and in the end this comes to be just what we find it, the 

 very ground upon which we build our houses and in which we 

 dig onr wells. 



In Fig. 3 we have a somewhat more complex section dia- 

 grammed, representing a state of things much more usual than 

 the very simple conditions described in Figs, i and 2. 



Fig. 3. 



Here we have the rocky substratum R, more or less con- 

 torted throughout, and upheaved as a mountainous ridge at 

 R3. Conformable to the surface of the rock, but of varying 

 thickness, we have a stratum of gravel, G, which crops out on 

 the surface between i and 2. Lying on this gravel is a layer of 

 clay, C, which varies in thickness, and comes to the surface at 

 2. Overlying this, is the soil,S. The line B^B^, represents, as 

 before, the mean level of ground water, with a gentle slope 

 towards the drainage stream D. The rain, which falls on the 

 region 2 to 3, supplies this ground water, which is tapped by 

 the wells, Wi, W^, Ws. It is at once evident why a well at 

 W4 remains dry, or only contains water when the season is 

 abnormally wet. The rainfall on the rocky surface to the right 



