60 



ERA OF THE OOLITE. 



kingdoms, but are always most conspicuous in families 

 approaching in character to those classes to which the full 

 organs are proper. This subject will be more particularly 

 adverted to in the sequel. 



The highest part of the oolitic formation presents some 

 phenomena of an unusual and interesting character, which 

 demand special notice. Immediately above the upper 

 oolitic group in Buckinghamshire, in the vicinity of Wey- 

 mouth, and other situations, there is a thin stratum, usually 

 called bv workmen the dirt-bed, which appears, from in- 

 contestable evidence, to have been a soil, formed, like 

 soils of the present day, in the course of time, upon a sur- 

 face which had previously been the bottom of the sea. 

 The dirt-bed contains exuviae of tropical trees, accumu- 

 lated through time, as the forest shed its honors on the 

 spot where it grew, and became itself decayed. Near 

 Weymouth there is a piece of this stratum, in which 

 stumps of trees remained rooted, mostly erect, or slightly 

 inclined, and from one to three feet high ; while trunks 

 of the same forest, also silicified, lie imbedded on the sur- 

 face of the soil in which they grew. 



Above this bed, lie those which have been called the 

 Wealden, from their full development in the Weald of 

 Sussex ; and these as incontestably argue that the dry 

 land forming the dirt-bed had next afterwards become the 

 area of brackish estuaries, or lakes partially connected 

 with the sea; for the Wealden strata contain exuviae ot 

 fresh water tribes, besides those of the great saurians and 

 chelonia. The area of this estuary comprehends the whole 

 south-east province of England. A geologist thus confi- 

 dently narrates the subsequent events : "Much calcareous 

 matter was first deposited, [in this estuary,] and in it were 

 entombed myriads of shells, apparently analagous to those 

 of the vivipara. Then came a thick envelope of sand, 

 sometimes interstratified with mud; and, finally, muddy 

 matter prevailed. The solid surface beneath the waters 

 would appear to have suffered a long continued and gra- 

 dual depression, which was as gradually filled, or nearly 

 so, with transported matter ; in the end, however, after a 

 depression of several hundred feet, the sea again entered 

 upon the area, not suddenly or violently — for the Weal- 

 den rocks pass gradually into the superincumbent creta- 

 ceous series — but so quietly, that the mud containing the 

 remains of terrestrial and fresh-water creatures was tran- 



