138 PLYMOUTH INSTITUTION. 



the animal and vegetable productions of the same countries at 

 different geological periods. 



The lecturer concluded his paper by producing maps and 

 diagrams to prove that England owes her insular situation to 

 agencies now in operation. He thinks that at" some compara- 

 tively recent geological period, England was joined to the Con- 

 tinent by an Isthmus near Dover, and that in those days extraor- 

 dinary high tides of 102 feet, obtained to the westward of the 

 Isthmus : and that inferior tides obtained in the German Ocean : 

 that the constant chafing of the waves, gradually diminished the 

 distance across; that equinoctial tides accompanied by equinoc- 

 tial gales, and great diminution in the pressure of the atmosphere 

 would produce exceedingly high tides in this locality, whereby a 

 breach might be made, and a torrent precipitated into the German 

 Ocean; bearing along with it, all the flints, gravel, chalk, sand, 

 and mud that composed the isthmus. These materials would 

 be deposited in a succession of banks, bearing some relation to 

 the velocity of the tide, as it gradually diminished as the distance 

 from the Strait increased ; now this is exactly what we find here, 

 for a series of shoals extending along the coast, from the Straits 

 of Dover to the Texel exist ; those nearest to Calais, being com- 

 posed of the most coarse and hard materials, and those further 

 to the eastward being of softer and more soluble n:atter. An 

 opening being once made, a total change took place in the range 

 of the tide, and in the direction of its streams; lands that were 

 once covered by the tide in the English Channel, would now be 

 left 40 feet above high water mark; other lands on the shores of 

 the German Ocean, would now be drowned by the tides: 

 because, before the disruption, the North Sea could only be 

 filled by a tide wave passing between Scotland and Norway, 

 whereas, after the disruption, another tide wave passed into the 

 North Sea, through the Straits of Dover. Now in some localities, 

 these tide waves would combine to produce higlier tides, whereas, 

 in other localities, they might become tides of interference and 

 mutually destroy each other; all the consequences resulting from 

 such a catastrophe are too numerous for us to mention. We 

 shall therefore conclude this notice in the lecturer's own words. 

 " We may, however, conclude, that the external crust of our 

 earth is continually but slowly changing its geological and geo- 

 graphical features, by the various agencies now in operation. 

 Water is raised, by heat, into steam, and mounts into the atmos- 

 phere to form clouds, which are wafted by the winds to the 



