294 Dr. Fleming on a [April, 



this subsidence happened (near 1000 years since at least), may 

 convince us, that when earthquakes happen, it is well for the 

 country that they are attended with subsidences.; for then the 

 ground settles, and the inflammable matter, which occasioned 

 the earthquake, has no longer room to spread, unite and recruit 

 its forces, so as to create frequent and subsequent earthquakes ; 

 whereas, where there are earthquakes without proportional 

 subsidences, there the caverns and ducts under ground remain- 

 ing open and unchoaked, the same cause which occasioned 

 the first has room to revive, and renew its struggles, and to 

 repeat its desolations and terrors ; which is most probably the 

 case of Lisbon." Phil. Trans. 1757, p. 52. 



The views of Dr. Borlase, in reference to this depression of 

 the ground, in consequence of earthquakes, was evidently in- 

 fluenced by the curious observations which he had formerly 

 made on the subsidence of some places at the Scilly Islands, 

 as stated, Phil. Trans, vol. xlviii. p. 62 ; and other observers 

 may be led to form the same opinion, especially if the singular 

 sinking of the cliff at Folkstone, about forty feet, even in the 

 absence of an earthquake, be taken in consideration. See 

 Phil. Trans. 1786, p. 220. 



Dr. Correa de Serra also ascribes the depressed position of 

 the submarine forest of Lincolnshire to the force of subsidence, 

 aided by the sudden action of earthquakes. " There is a force 

 of subsidence (he says) (particularly in soft ground), which, 

 being a natural consequence of gravity, slowly, though per- 

 petually operating, has its action sometimes quickened and 

 rendered sudden by extraneous causes, for instance, by earth- 

 quakes." " This force of subsidence, suddenly acting by means 

 of some earthquake, seems to me the most probable cause to 

 which the actual submarine situation of the forest we are speak- 

 ing of may be ascribed. It affords a simple easy explanation 

 of the matter ; its probability is supported by numberless in- 

 stances of similar events." Phil. Trans. 1709. 



Professor Playfair, when contemplating the phenomena of 

 the Lincolnshire submarine forest, rejected the explanation 

 offered by Dr. Correa de Serra, and availed himself of some of 

 the peculiar assumptions of the Huttonian Theory of the Earth. 

 " The subsidence (he says) however, is not here understood 

 to arise from the mere yielding of some of the strata imme- 

 diately underneath, but is conceived to be a part of that geolo- 

 gical system of alternate depression and elevation of the surface, 

 which probably extends to the whole mineral kingdom. To 

 reconcile all the different facts, I should be tempted to think, 

 that the forest which once covered Lincolnshire, was immersed 

 under the sea by the subsidence of the land to a great depth, 

 and at a period considerably remote ; that when so immersed, 

 it was covered over with the bed of clay which now lies upon 



