THE TERTIARY SYSTEM. 743 



not the appearance of anything natural. Deep purplish red, dusky blue, bright ochreous 

 yellow, grey nearly approaching to white, and absolute black, succeed each other, as 

 sharply defined as the stripes in silk ; and after rain, the sun shining upon the cliffs 

 gives a brilliancy to some of these colours, rivalling the resplendence of real silk when 

 high lights are thrown upon it. 



The Paris basin is larger than either of the preceding, and more remarkable on account 

 of the abundance of its organic contents, which, examined by die genius of Cuvier, gave 

 birth to true philosophical geology. It includes an area of more than seven thousand 

 square miles around the capital, and forms an irregular polygon, elongated from north to 

 south, the Loire flowing through its southern confine, and the Seine pursuing a winding 

 course through the middle, nearly dividing it into two equal parts. The greatest extent 

 of the basin, from north to south, is about 180 miles, and 100 miles from east to west. 

 The site of Paris is nearly centrical. The sides of the polygon pass in the vicinity of 

 the towns of Laon, Clermont, Chartres, Vendome, Blois, Orleans, Epernay, and Eheims. 

 Everywhere, within these limits, the strata rest upon chalk, which is visible at the surface 

 beyond them, and forms a great belt around the tertiary deposits. The Paris basin com 

 prises a quintuple series of formations, two of marine, and three of fresh-water origin, 

 which alternate with each other in the following order : 



f Marls interstratified with layers of flints, one series of layers without shells, 

 upper iresn- water group. "5 , . . , 



I and the other replete with them. 



f Beds of micaceous sand and sandstone, loosely aggregated, except at Fontaine- 

 Upper marine group. u-TuTI . 



L bleau, and commonly white, but sometimes slightly red or yellow. 



r Calcaire silicieux, a siliceous limestone resembling a precipitate from the 



Second fresh-water group. < waters of mineral springs ; marls ; gypsum, with abundant bones in the 

 L hill of Montmartre, near Paris. 



f Calcaire grassier, a coarse limestone, and green-sands, containing the greater 

 icond marine group. | proportion of the shells of the Paris basin> 



f Plastic clay and sands ; beds of lignite, and pebbly beds, of partial extent 

 Third fresh-water group. \ and ]ing ^ ia occurrence . 



It is clear, that to account for the phenomena of these formations, we must have 

 recourse to the hypothesis that the sea once occupied that depression in the chalk which 

 is now filled up with tertiary strata ; that the ocean probably flowed into it from the north, 

 as into a bay or gulf, while a river or rivers charged with argillaceous sediment, drifting 

 down, also, fresh-water shells and terrestrial plants, entered it from the south ; and that this 

 aspect of the district was repeatedly modified through a long series of ages, the relations of 

 land and sea being changed, and extensive vicissitudes occurring, till the final elevation of 

 the deposits to their present position transpired. But passing by the mutations of inanimate 

 nature indicated in this district, we have a large assemblage of organic remains in the 

 Paris basin unfolding new and interesting forms of life. The coarse limestone, calcaire 

 grassier, is remarkable for containing shells belonging to an immense number of species, 

 upwards of 400 distinct species having been collected from it in one locality ; but it is 

 also remarkable for its great abundance of species belonging to the genus Cerithium 

 which occur, measuring from ten to fourteen inches in length. M. Deshayes states 

 the number of species in the Paris basin at 137, almost all of them found in the 

 calcaire grossier. The living specimens of this genus are met with in the Mediterranean, 

 along the shores of Australia, and the west coast of Africa ; and Sir C. Lyell makes the 

 remark, that they inhabit the sea near the mouths of rivers, where the water is brackish, 

 so that their abundance in the marine strata of the Paris basin is an interesting corro- 

 boration of the hypothesis advanced respecting it. 



But what has conferred special celebrity upon the locality we are noticing, are the 

 remains exhumed from the fresh-water formation of gypsum and gypseous marls, which 



