Ch. XIII.] CRAG OF ENGLAND. 



173 



are in great part horizontal, or slightly undulating ; but at 

 some points they are much disturbed, especially where several 

 masses of chalk appear to have been protruded from below. 



The annexed section may give a general idea of the manner 

 in which the crag may be supposed to rest on the chalk as we 

 pass from the Norfolk cliffs, at Trimminghani, into the interior, 

 where the country rises gradually. 



No. 30. 



a, Chalk. b } Crag. c, Lacustrine deposit. 



D, Trimmingham beacon. E, Interior and higher parts of Norfolk *. 



The outline of the surface of the subjacent chalk, in this 

 section, is imaginary, but is such as might explain the relations 

 of those protruded masses, three of which appear in the cliffs 

 near Trimmingham, and which some geologists have too hastily 

 assumed to be unconnected with the great mass of chalk below. 

 We shall treat of these presently, when we describe the dis- 

 turbances which the crag appears to have suffered since its 

 original deposition. 



In the interior, at E, there is a thick covering of sand and 

 gravel upon the chalk, having the characters of an alluvium, 

 partly, perhaps, marine, and partly terrestrial, and which seems 

 to pass gradually in this district into the regular marine strata 

 of the crag. 



Forms of stratification. In almost every formation the in- 

 dividual strata are rarely persistent for a great distance, the 

 superior and inferior planes being seldom precisely parallel to 

 each other ; and if the materials are very coarse, the beds often 

 thin out if we trace them for a few hundred yards. There are 

 also many cases where all the layers are oblique to the general 



* This section is compiled principally from one by Mr. Murchison, the others in 

 this chapter are from drawings by the Author. 



