306 RAMBLES OF A NATURALIST. 



Does anything analogous to this occur in this gulf, 

 and is its gradual filling up even partially owing to a 

 progressive elevation of the district above its ancient 

 level ? This question is so much the more admis- 

 sible, as positive facts attest at several points the 

 recent action of those geological forces which are 

 incessantly modifying the thin pellicle which we call 

 terra jfirma. In the environs of Fontenay, in the 

 very midst of the marshes whose origin we have 

 described, exist deposits of shells well known to 

 geologists under the name of the banks of Saint- 

 Michel-en-PHerm. These extensive banks are com- 

 posed of the shells of oysters, mussels, and pectens, 

 belonging to the same species that occupy the 

 neighbouring seas.* All these shells are appa- 

 rently retained in their original position ; a great 

 many of them have their valves connected by the liga- 

 ment which completes the hinge, and they have not 



four feet during every century at those points at which it is the 

 most rapid. 



On the other hand, it would appear from marks made upon the 

 coast of Scania in the time of Linnseus, that this part of the shore 

 is gradually sinking below the water. The same phenomenon is 

 manifested on the coast of Greenland, over an extent of more than 

 600 miles. Buildings placed upon low islands, or upon the con- 

 tinent, have been submerged, while it has been found necessary at 

 different times to remove farther inland the establishments erected 

 on the beach. It is therefore probable that on these regions the 

 earth's crust presents at the present day one of those movements 

 giving rise to the flexure of strata, which modern geologists appear 

 to agree in regarding as an important feature in geological pheno- 

 mena. 



* The three banks of Saint- Michel-en-THerm are about 730 

 yards in length and 300 yards in width, rising from ten to fifteen 

 yards above the level of the surrounding marshes* 



