90 VESTIGES OF THE 



their brain, deficient in the organs connecting the two 

 hemispheres — and in the mode of gestation, which is only 

 in small part uterine — this family is clearly a link 

 between the oviparous vertebrata (birds, reptiles, and 

 fishes) and the higher mammifers. This is further 

 established by their possessing a faint development of 

 two canals passing from near the anus to the external 

 surface of the viscera, which are fully possessed in 

 reptiles and fishes, for the purpose of supplying aerated 

 water to the blood circulating in particular vessels, but 

 which are unneeded by mammifers. Such rudiments of 

 organs in certain species which do not require them in 

 any degree, are common in both the animal and vegetable 

 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 par- 

 ticularly 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 Weymouth, and other situations, there is a thin 

 stratum, usually called by workmen the dirt-heel, which 

 appears, from incontestable evidence, to have been a soil, 

 formed, like soils of the present day, in the course of 

 time, upon a surface which had previously been the 

 bottom of the sea. The dirt-bed contains exuvias of 

 tropical trees, accumulated through time, as the forest 

 shed its honours on the spot where it grew, and became 

 itself decayed. Near Weymouth there is a piece of this 

 stratum, in which stumps of trees remain rooted, mostly 

 erect or slightly inclined, and from one to three feet 

 high ; while trunks of the same forest, also silicified, 1 



le 



imbedded on the surface of the soil in which they grew: 



