98 Transactions of the Royal Society of South Africa. 
The wells are situated over 160 miles from the coast, at an altitude of 
over 2,700 feet above sea-level. High water at Tarka Bridge occurs 
about 14-|- hours after high water at East London, while the lag in the 
case of low water is nearly 15 hours. 
The principal conceivable theories to account for the phenomena 
would appear to group themselves in three classes : — 
A. Theories depending on the direct gravitative influence of the 
sun and moon on the land or the underground water. 
B. Theories depending on the action of the marine tides on the 
coast loading and distorting the land. 
C. Theories depending on the action of marine tides in periodically 
reducing the freedom of outflow of underground water through 
submarine springs. 
No attempt is at present made to state or discuss these theories. It is 
felt that a satisfactory theory can be arrived at only by the co-operative 
discussion of the subject by astronomers, geologists, and hydraulicians. 
Tidal wells are known in many parts of the world, but practically all 
are within 3 or 4 miles of the seashore and at no considerable altitude. 
The records from the Orisino Bore in Australia do not show the periodicity 
of marine tides. 
One case is reported at Lille in France, 40 miles from the coast, but 
at no great height above sea-level. The evidence supporting the tidal 
claim of this well is far from satisfactory. 
It is believed that there is no other record of an inland well showing 
fluctuations of true lunar periodicity. 
