lO GEOLOGICAL NOTES 



or more or less peaty clay or mud, with shell marl, intervene 

 between them. And it seems clear to me that the gravel has 

 always been brought down in the channel of the stream ; and 

 that the surface loam is the mud which has been deposited on 

 the surface during floods and very high tides. Where, between 

 the gravel and the loam, there is a considerable thickness of 

 peat, the plants, the remains of which compose it, having grown 

 in situ, there shallow backwaters must have existed in which 

 the plants grew. On the other hand, the irregular masses of 

 vegetable matter mixed more or less with gravel and sand have 

 evidently been brought down a channel, mainly in time of flood. 

 And the little land and fresh-water molkisca, composing the shell 

 marl, flourished either in backwaters or in shallow parts of a 

 main stream where sand or mud were being deposited close to 

 one bank, while that on the opposite side was suffering from 

 erosion. The steady continuance of a state of things of this 

 kind, at any one spot, for many years, would bring into existence 

 a band of shell marl having a breadth corresponding to the 

 lateral deflection of the channel of the stream. 



I 



Fig. 7. New Reser\oirs Section of Minor Channel in Southern Reservoir 



(1901). I. Gravel; 2. Mud; 3. Peat, with man}- Plant-stems ; 4. Sand with 



Shells in channel; 5. Surface Loam. Height of Section, 10 to 11 ft. ; 



length, about 18 yards. 



The section across the old channel, shown in Fig. 5, illus- 

 trates my remark that the constant constituents of a section are 

 the gravel towards the base and the loam at the surface. Taking 

 the height of the section as loft., then the changes are all in the 

 5ft., or thereabouts, of beds in the middle part; the gravel 

 towards the base and the loam at the surface remain unaltered 

 throughout. This is especially noteworthy in the case of the 

 loam, and clearly indicates that it is a deposit resulting from a 

 general cause which, like a flood, would affect a whole river 

 valley. It would consequently not be affected by the local 

 character of the beds on which it rested, and would tend to 

 equalise the surface levels, as we know it does. 



