80 TOWN GEOLOGY. [in. 



First appear thin layers of a very hard blue lime- 

 stone, full of shells, and parted by layers of blue mud. 

 That rock runs in a broad belt across England, from 

 Whitby in Yorkshire, to Lyme in Dorsetshire, and is 

 known as Lias. Famous it is, as some readers may 

 know, for holding the bones of extinct monsters 

 Ichthyosaurs and Plesiosaurs, such as the unlearned 

 may behold in the lake at the Crystal Palace. On 

 this rock lie the rich cheese pastures, and the best 

 tracts of the famous ' ' hunting shires " of England. 



Lying on it, as we go south-eastward, appear 

 alternate beds of sandy limestone, with vast depths of 

 clay between them. These "oolites," or freestones, 

 furnish the famous Bath stone, the Oxford stone, and 

 the Barnack stone of Northamptonshire, of which 

 some of the finest cathedrals are built a stone only 

 surpassed, I believe, by the Caen stone, which comes 

 from beds of the same age in Normandy. These 

 freestones and clays abound in fossils, but of kinds, 

 be it remembered, which differ more and more from 

 those of the lias beneath, as the beds are higher in 

 the series, and therefore nearer. There, too, are 

 found principally the bones of that extraordinary 

 flying lizard, the Pterodactyle, which had wings 

 formed out of its fore-legs, on somewhat the same 

 plan as those of a bat, but with one exception. In 

 the bat, as any one may see, four fingers of the hand 

 are lengthened to carry the wing, while the first alone 

 is left free, as a thumb : but in the Pterodactyle, the 

 outer or " little " finger alone is lengthened, and the 

 other four fingers left free one of those strange 

 instances in nature of the same effect being produced 

 in widely different plants and animals, and yet by 



