24 DESCRIPTION OF THE STRATA. 



especially as the thickness of the bed of gravel at that spot, and the 

 slope which it must have from the chalk hills towards the sea, cor- 

 responding with the dip of the strata, must gi-ve great facility to that 

 accumulation. Nor is it less difficult to conceive, why the water at 

 the spring is never brackish ; for though the force, or weight, of the 

 fresh water current, is insufficient to clear its passage into the ocean, 

 when opposed by the weight of the rising tide, it may be fully adequate 

 to stem the opposing current of salt water, so as never to allow it to 

 reach the spot where the tube is inserted ; especially if, as is proba- 

 ble, the sea outlet be at a great distance, and the passage to it be 

 intricate, winding, and parted into several channels. The same con- 

 siderations, viewed in connection with the comparative lightness of 

 fresh water, may enable us to understand, why the water in the 

 spring rises so much higher than the level of the tide. 



This ebbing and flowing spring is not the only phenomenon of 

 the kind. At the mouth of the river Loe in Cornwall, there is a fresh 

 water lake which communicates with the sea by a subterraneous pas- 

 sage. The water rises and falls with the tide, yet is always fresh. 

 An instance of the same kind has been observed in New Holland.* 



Strange as this phenomenon may appear, it is not more strange 

 than some of the notions advanced to explain it. Since the discovery 

 of the spring, various writers have published, in the literary periodical 

 works, descriptions of the facts observed, accompanied with theories 

 proposed to account for them.t Some of these explanations nearly 

 coincide with the solution given above. Others proceed on supposi- 

 tions that are wild and improbable. One hypothesis, in particular, 

 is so extravagant, and rests on assumptions so inconsistent with 

 facts, that it may be pi'oper to notice it, in order to correct the mis- 

 takes connected with it. 



* See Geological Transactions^ Vol. I. p. 140, 141. 



t Pbilosoph. Trans, for 1815, Pt. I. Philos. Journal XLV. p. 66 & 432. XLIX. p. 230. 

 I-. p. 81—83, 200—203, 267, 268. Repertory of Arts Vol. XXX. p. 342, &c. 



