xiv 



CONTENTS. 



I Page. 



to those of Tropical Climates found in the Sussex Beds... Supposed Appearance 

 of the Country when these Animals fiouiished....Petvvorth Limestone.. ..Hast- 

 ings Sand and Weald Clay. ...The V/ealden Beds formerly furnished the great- 

 est Part of the Iron manufactured in England. ...Mr. Mantell's Enumeration of 

 the Species of Terrestrial and Freshwater Fossil Remains in the Wealden Beds. 

 ....Observations on the Wealden Beds, and the Change from Marine to Fresh- 

 water Formations, - 191 



CHAPTER XIV. 



ON CHALK, AND THE SUBJACENT BEDS OF GREEN SAND,, 



Extent of the Chalk Formation. ...Green Sand divided into lower and upper 

 Green Sand by a Bed of Clay called Gait ...Chalk Marl. .. .Chalk ; its Mineral 

 Characters. ...Change of Character in the Alps.. ..Flints in the upper Chalk.... 

 On the Formation of Flints. ...Remarkable Organic Remains in Chalk. ...Recent 

 Discovery of Beds belonging to the Chalk Formation, in the United States of 

 America. ...On the Scaglia of the Alps supposed to represent Chalk, - 200 



CHAPTER XV. 



ON THE FORMATION OF SECONDARY LIMESTONE AND SANDSTONE, AND 

 ON THE PROGRESSIVE DEVELOPEMENT OF ORGANIC LIFE. 



On the Deposition of Chalk. ...Whether formed by Animal Secretion, or by 

 Eruptions of Water holding calcareous Earth in Suspension or Solution. ...Mud 

 Volcanoes.. ..Animal Bodies suddenly encased in Chalk indicate the Time re- 

 quired to form a Stratum of a given Thickness. ...Oolite and Encrinal Limestone 

 partly formed by Animal Secietion... .Formation of Sandstone. ...Repeated Ap- 

 pearance of dry Land during the Epoch when the Secondary Strata were de- 

 posited. ...Progressive Developement of Organic Life in the Secondary and Ter- 

 tiary Epochs.. .-Disappearance of enormous Reptiles and chambered Shells from 

 the Seas of Northern Latitudes.. ..Probability of the Ichthyosaurus existing as a 

 living Species in the present Seas, - - . . . 206 



CHAPTER XVI. 



ON THE LOWER OR MORE ANCIENT TERTIARY STRATA, 



Formation of Tertiary Strata in Lakes or Inland Seas. ...Lakes of North 

 America. ...Falls of Niagara. ...Alternations of Marine and Freshwater Strata.... 

 Arrangement of the Tertiary Strata in the Paris Basin. ...Plastic Clay and Lon- 

 don Clay. ...Geology of the lower Vale of the Thames. ...Remains of Crocodiles 

 and the Nautilus in London Clay....Mo]asse of Alpnach in Switzerland, with 

 Coal and Teeth of the Mastodon.... Ca/caire Grassier, or Coarse Limestone of 

 the Paris Basin, supposed to be of the same Age as the London Clay.... CaZ- 

 caire Siliceux.... Gypsum and Gypseous Marl of the Paris Basin, containing 

 Bones of numerous extinct Species of Land Quadrupeds. ...Remarks on their 

 Discovery and Organization by Baron Cuvier.... Marine Sandstone... Millstone. 

 ... Upper Freshwater Formation. ...Tertiary Strata in the Isle of Wight. ...Crag 

 of Norfolk,. ...its true Geological Position not determined. ...Cliffs of Bi ighton, 215 



CHAPTER XVIL 



ON THE RECENT TERTIARY STRATA, OR WHAT ARE CALLED BY SOME 

 GEOLOGISTS QUATERNARY. 



The Methods for determining the relative Age of Formations explained, and 

 their Value examined... Evidence from Position. ...Evidence from Organic Re- 

 mains.. ..System of M. Deshayes founded on Fossil Shells. ...Uncertainty at- 

 tending the Evidence from Organic Remains.... Ai bitrary Classifications of Nat- 

 uralists.. ..Supposed Limits to the Transmutation of Species of Molluscous An- 

 imals examined.. ..System of M. Eliede Beaumont.. ..Geological Age of Palaeo- 



