GEOLOGY. 91 



found in this group. The Echinus, or Sea hedge-hog, is 

 very abundant ; as are also Ammonites. 



Sauroid fishes are also numerous in this formation, 

 and among the reptiles, the MEGALOSAURUS, or GIANT 

 LIZARD, is the most remarkable. This was an enormous 

 carnivorous animal, 4O or 50 feet long and 1<2 feet high, 

 and formed for inhabiting the land. The PTERODACTYLE 

 is also found in this group. This animal had the head 

 of a bird, the wings of a bat, and its body and tail like 

 those of the Mammalia. Its eyes were of an enormous 

 size, so as to enable it to fly by niglit. Its size varied 

 from that of a snipe to that of a cormorant. It appears 

 to have been able to live either on the earth, in the air, 

 or in the water. Dr. Buckland observes, " With flocks 

 of such like creatures flying in the air, and shoals of no 

 less monstrous Ichthyosauri and Plesiosauri swarming in 

 the ocean, and gigantic crocodiles and tortoises crawling 

 on the shores of the primeval lakes and rivers, the air, 

 sea, and land must have been strangely tenanted in 

 those early periods of our infant world." 



WEALDEN BEDS. The Wealden is a freshwater for- 

 mation or deposit, and, very singularly, lies between two 

 marine formations. This formation takes its name from 

 the TTeulds of Kent, where it particularly occurs, and 

 extends over a vast tract of the southern part of Eng- 

 land, and is from 800 to 900 feet thick. Its subdivisions 

 are Weald clay, including beds of sand and shelly lime- 

 stone ; Hastings sand, in which occur clay and calcareous 

 grits ; and Purbe(k beds, consisting of limestone and 

 marl. Between the inferior division of the Wealden 

 and the Portland stone, or upper member of the Oolite, 

 in Portland, there intervenes a layer of dark matter 

 from 12 to 18 inches thick, evidently an ancient vege- 

 table soil. Trunks of trees silicified, and remains 

 of plants, are buried in this Dirt-bed, as it is called. 



The Iguanodon, a reptile of a most gigantic size, has 

 been found in a fossil state in these beds. This animal is 

 said to have been from 50 to 80 or 90 feet in length. 

 The Iguanodon was a herbivorous animal, and resembled 

 the modern Iguana in having a horn on its nose. 



GREENSAND. The Greensand, according to some geo- 

 logists, forms a part of the Cretaceous group, and consists 



