4 J. L. LOBLET — CRETACEOUS ROCKS OF ENGLAND. 



Marlborough Downs, and the Chiltcm Hills, and then extends to 

 the north-east through this county, Cambridgeshire, Sulfolk, and 

 Norfolk, to the North Sea. The Norfolk Chalk, however, gives off, 

 as it were, a branch, which, after running through Lincolnshire, 

 widens into the Wolds of the eastern part of Yorkshire, then 

 contracts, until, at Flamborough Head, it terminates in a point. 

 Thus it will be seen that the Cretaceous rocks of England lie 

 almost wholly on the south-east side of a line drawn from Portland 

 Bill to Scarborough Castle Rock. 



Though the extension of the Cretaceous rocks is thus limited in 

 England, it must not be supposed that deposits of Cretaceous age 

 are nowhere else to be found. In North America they occur in 

 New Jersey, as stated by Sir Charles Lyell ; and in South America, 

 Charles Darwin considers that they are to be met with in various 

 parts of a region extending from Columbia north of the Equator as 

 far south as Terra del Fuego, and in the Andes, at very considerable 

 elevations, while beds of Cretaceous age are found so far to the 

 East as Pondicherry in India. Deposits of the same epoch were 

 not, however, necessarily of the same sea or ocean ; for at every 

 period of the earth's history there were doubtless large and small 

 seas, as at present, and during each geological epoch a dis- 

 tribution of land and sea prevailed, which was peculiar to that 

 period, and markedly different from that of the preceding or 

 succeeding epoch. The physical geography of the earth varied as 

 the ages rolled on, and became what we now find it only after a 

 succession of changes co-extensive with the age of the earth itself. 



The Cretaceous rocks, as a system, have been divided into several 

 minor groups of strata commonly called "formations," and named 

 chiefly from their lithological or physical characters. Thus we 

 have the Wealden, the Lower Greensand, the Gault, the Upper 

 Greensand, and the Chalk. 



The lowest of these great divisions, the "Wealden, is a formation 

 of peculiar interest, constituting as it does a distinct portion of our 

 island, and suggesting to the geologist a distribution of land and 

 sea strikingly different from that which now obtains. Though of 

 great thickness, variously estimated at 1300, IGOO, and 2000 

 feet, the Wealden group of rocks is of freshwater and estuarine 

 origin, being, in fact, au old delta of a great river which must have 

 flowed over a portion of the earth's surface now covered by the 

 sea. In England it forms the country lying between the North and 

 South Downs, but it is not confined to Avhat is called the AVealden 

 area. The most westerly locality where Wealden beds are seen is 

 Brook Point, in the Isle of Wight ; the most northerly, Shotover 

 Hill, near Oxford ; while on the Continent it is found constituting 

 the country near Boulogne ; and as far south as Vassy, deposits 

 assigned to the Wealden occur. So great a delta as must have 

 existed to leave these wide-spreading remains would bo the ac- 

 cumulated detritus brought down by a great river, and many are 

 therefore led to the conclusion that a continent existed where is 

 now the Atlantic Ocean, and that from this ancient laud came 



