Geology. — On the Order of Succession of Rocks, 339 



cal series have been found in their respective positions, wherever 

 they have been observed, still in no part of the world have all 

 the beds been found, in any one particular place, thus overlying 

 each other. In every part of the world some of them are want- 

 ing. In Europe, that groupe of beds called the oolitic series, or 

 calcaire da Jura according to the French, and which includes 

 Nos. 17 and 27, (Lias and Portland oolite) — with the interme- 

 diate beds, — of our Tabular View, is very common, but has not 

 yet been observed in North America : this groupe has an aver- 

 age thickness of 2700 feet, in England. The groupe including 

 Nos. 12 and 16, usually called the new red sand stone formation, 

 is common in Germany ; but in this last country it includes a 

 member for which no equivalent has yet been found in England, 

 viz. the Muschelkalk, which has an average thickness of 300 feet. 

 The defective distribution of particular beds in various parts of 

 the world, affords, however, no argument against the successive 

 order in which all the beds have come to their places in the se- 

 ries; for wherever they are found, they are constant in their re- 

 lative succession to each other. The occasional absence then of 

 particular beds, is to be attributed to causes which are the legi- 

 timate objects of geological research. Without practical inves- 

 tigations, we are not authorized to say, that the absence of any 

 bed is a casus omissus, occasioned by the local deficiency of the 

 causes which have produced the bed in other places ; because 

 the bed may have been deposited, and have subsequently disap- 

 peared, through the agency of causes which have frequently 

 changed the condition of the surface of the earth, by wasting 

 extensive portions of it. 



The chalk, which in some parts of Europe has an average 

 thickness of 700 feet, is remarkable, above all other beds, for 

 containing, in the upper part of its white mass, irregular beds of 

 nodules of dark coloured flint. We remember standing on the 

 summit of Ilaldon Hill in Devonshire, England, half way be- 

 tween the city of Exeter and the coast, whence one of the most 

 magnificent views in Europe is to be enjoyed, and replete with 

 geological interest. At the foot of the hill lies a rich and broad 

 valley, with the river Ex flowing through it: to the right lies the 

 ocean. At a great distance in front, the chalk cliffs in Dorset- 

 shire are perceived. Haldon Hill is composed of green sand. No. 

 33, and is there lying on the red marie. No. 16; all the other 



