226 Tides Illustrative of Geological Phenomena. 



now regulate the deposition of sand-banks have been in ope- 

 ration during the diluvial, tertiary, and cretaceous epochs ; 

 the deposits of these epochs forming so many parallel zones 

 successively following the great backbone of the Alle- 

 ghanies. 



The diluvial deposits, in Europe as well as in America, 

 merit a special attention in this respect. No doubt, during 

 the diluvial epochs, the plains of Northern Germany, as well 

 as a great part of Scandinavia, and, on this continent, the 

 coast of the United States from Florida to Canada, formed 

 a series of banks and shoals, like the banks of Newfound- 

 land in our day, whilst the plains of the west, between the 

 Alleghanies and the Rocky Mountains, formed a vast bay, 

 comparable to the Gulf of Mexico, in which the sea deposited 

 the fine sand and clay of the prairies, as it now deposits in 

 the Gulf of Mexico the sand and mud that border the coast 

 of Texas. 



The results of the above researches may be summed up 

 thus : — 



1^^, The form and distribution of banks, and of alluvial 

 formations in general, are, in a great measure, dependent 

 on tides. They ought to be found everywhere where the 

 tidal current is sufficiently abated to permit the materials held 

 in suspension to be deposited. The finer and lighter mate- 

 rials must therefore be deposited in the calmer places. 



2d, The formation of submarine banks is indispensable to 

 the maintenance of animal life, since they constitute the most 

 favourable localities for marine animals. 



3o?, The formation of deltas at the mouths of rivers is in 

 an inverse ratio to the force of the tide. 



4:thi The sedimentary deposits of the most recent geologi- 

 cal epochs being, in all respects, like the alluvial deposits 

 of our day, we must hint that they were formed under the 

 operation of the same laws. 



5M, The form and extent of continents, so far as they are 

 composed of sedimentary deposits, are thus dependent on as- 

 tronomical laws, that is, on the attraction which the moon 

 and the sun exert, and in all time have exerted on the liquid 

 part of our planet. — {Besor^in Massachusetts Quarterly Be- 

 vierv for December 1848.) 



