450 LOUIS AGASSTZ. 



tions, is several inches in thickness. The 

 leaves of this plant, some specimens of which 

 I inclose, are so well preserved that many 

 still retain their green tint and even show the 

 vessels and the grains of chlorophyll within. 

 You would say the sea might have thrown 

 them there only a few days since, so fresh do 

 they seem ; they might serve as stable litter, 

 and yet they date back to the deposition of 

 the drift, for the deposit which covers them 

 is the same as that below them. Except the 

 bed of zostera, deposited, no doubt, during a 

 temporary encroachment of the sea, there is 

 no other sign of the action of the water in 

 all this part of the hill. Among the leaves 

 of the zostera were found the greater part of 

 the shells which now live along the coast and 

 attach themselves upon this sea-weed, such as 

 the Littorina rudis, Lacuna vincta, Lottia al- 

 veus, Mytilus plicatulus jeune, Spirorbis nau- 

 tiloides ; small polyps also, among others Tu- 

 bulipora patina. Beside these, I have also 

 found among them broken pieces of Limulus 

 polyphemus and fragments of wood. 



Thirty feet lower, that is to say, about 

 twenty feet above the sea-level, on the south- 

 ern slope of the hill, Mr. Desor found a bed 

 of shells, extending all along the shore, essen- 



