W E A 



[461 



W E K 



with limestone almost wholly com- 

 posed of freshwater snail- shells, 

 occupy the uppermost place ; sand 

 and sandstones, with shales and 

 lignite, prevail in the middle; 

 while in the lowermost, argillaceous 

 beds, with shelly marbles or lime- 

 stones, again appear; and, buried 

 beneath the whole, is a petrified 

 forest, in which the trees are still 

 standing, and the vegetable mould 

 undisturbed. The organic remains 

 of the "Wealden consist of leaves, 

 stems, and branches of plants of a 

 tropical character ; bones of enor- 

 mous reptiles of extinct genera ; of 

 crocodiles, turtles, flying reptiles, 

 and birds ; fishes of several genera 

 and species, and shells of a fluvia- 

 tile character. The vegetable re- 

 mains belong, some of them, to 

 plants which appear to have held 

 an intermediate place between the 

 Equiseta and Palms, as the Clath- 

 raria ; while others approach to 

 arborescent ferns, the species being 

 very peculiar, and not known in 

 any other deposit, whether of 

 higher or inferior antiquity. For 

 a knowledge of that enormous rep- 

 tile, the Iguanodon, we are entirely 

 indebted to the indefatigable and 

 scientific researches of Dr. Man tell. 

 WEA'THERING. A term used to ex- 

 press the action of the atmosphere, 

 rain, &c., on the surface of rocks. 

 There is no rock, even the hardest, 

 that does not bear some marks of 

 what has been termed weathering. 

 The amount of surface-change, so 

 produced, is exceedingly variable, 

 depending much on local causes. 

 The tors of Dartmoor, Devon, may 

 be referred to as excellent examples 

 of the weathering of a hard rock. 

 The weathering of these tors is so 

 exceedingly slow, that the life of 

 man will scarcely enable him to 

 perceive a change; therefore the 

 period requisite to produce their 

 present appearances must have been 

 very considerable. Variations in 



temperature much assist the chem- 

 ical decomposing power of the 

 atmosphere. 



"WEDGE-SHAPED. In botany, applied 

 to leaves that are broad at the 

 summit and gradually taper toward 

 the base. 



WEIGHT OP THE ATMOSPHERE. The 

 air is an elastic fluid resisting pres- 

 sure in every direction, and is sub- 

 ject to the law of gravitation. The 

 pressure of the atmosphere is cal- 

 culated to be about fitteen pounds 

 to every square inch, so that the 

 surface of the globe sustains a 

 weight of 11,449,000,000 hundreds 

 of millions of pounds. 



WE'NLOCK FORMATION. The lower for- 

 mation of the upper Silurian rocks, 

 comprising the Wenlock limestone 

 and Wenlock shale. 



WE'NLOCK LIMESTONE. The upper 

 subdivision of the Wenlock forma- 

 tion. The Wenlock limestone, 

 says Sir E. Murchison is in every 

 respect identical with the well 

 known rock of Dudley, and con- 

 tains the same organic remains. 

 The colour of the rock is usually 

 grey, but the crystalline varieties 

 are sometimes dark blue, and more 

 rarely pink, the mass being freckled 

 with veins and strings of white 

 crystallized carbonate of lime. The 

 simple minerals hitherto observed 

 in the Wenlock limestone of Shrop- 

 shire, consist of crystallized car- 

 bonate of lime in various forms, 

 sulphate of barytes, sulphurets of 

 iron, peroxide of manganese, crys- 

 tals of copper pyrites and bitumen. 

 As regards the organic remains 

 hitherto discovered, the most strik- 

 ing zoological feature consists in 

 the vast number of contained corals. 

 The most prevalent of these are 

 Heliopora pyriformis ; Catenipora 

 escharoides ; Stromatopora concen- 

 trica ; Pavosites gothlandica ; Cya- 

 thophyllum turbinatum; Limaria 

 clathrata, &c. Among the mollusks 

 and conchifers may be enumerated 



