ALLUVIAL COVERING. 2^ 



and constructed a reservoir, &c. for the use of the town and shipping. 

 There is no discharge from the tube, till the tide has risen to such a 

 height as to be only about four feet lower than its orifice; and when 

 the sea has again subsided to the same level, the stream ceases ta 

 flaw till the return of the next tide ; the discharge continuing four or 

 five hours eaeh flood. In high tides, the stream, as may be expected, 

 flows longer than usual : and after great rains the discharge is both 

 more copious, and more prolonged; being kno^vn to commence when 

 the level of the tide is about eight feet below the mouth of the tube. 

 When there is a heavy sea on the coast, an undulation is observable 

 in the discharge of the water. 



The most easy and obvious way of accounting for these facts, is 

 by supposing, that this spring has an outlet towards the sea, probably 

 beneath low water mark; which outlet is open at low water, so far 

 as to permit the spring to empty itself into the sea, but is obstructed 

 or choaked up by the flood tide ; so that the fresh water, accumulat- 

 ing in its gravelly receptacle, bursts forth at the new opening which has 

 been made for it ; and continues to flow from thence, till the falling 

 of the tide permits it to resume its original passage. As the obstrucr 

 tion of this passage will gradually increase as the tide rises, and di- 

 minish as it falls, and be greatest at high water ; being according to 

 the weight of the sea water over the outlet, and the quantity of that 

 water pressing into that outlet, and forcing back, or stemming, the 

 current of the fresh water; the phenomena observed at the orifice of 

 the tube are just such as, on that supposition, might be expected. 

 The undulations occasioned by a storm, may be traced to the irregu- 

 larity of the pressure then felt at the sea outlet, the heavy waves 

 forcing the salt water into it by sudden jerks, and giving a corre- 

 sponding impulse to the fresh water then propelled before it. It is no 

 less natural to expect, after heavy rains, a larger accumulation of 

 fresh water, and consequently a more copious discharge at the spring; 



