§4. STRATIFICATION. 197 



trations of this structure. The original direction of these 

 layers must have been more or less horizontal, for this 

 obvious reason, that in their fluid state they would find 

 their own level, and spread over the surface of the basin 

 into which they flowed ; and although they might partake 

 of the inequalities of the depressions in which they were 

 deposited, yet this cause would not affect their general 

 distribution. The strata when accumulated in very thin 

 layers, resembling the seams formed by the leaves of a 

 closed book, are termed lamince ; a character that com- 

 monly prevails in fluviatile or river deposits : thus the 

 shales, clays, and sandstones, of Tilgate Forest are lami- 

 nated, and often bear the impress of the waves which have 

 flowed over them (see p. 60). 



The contemporaneous beds formed in the same oceanic 

 basin, though often maintaining a general character over 

 very extensive areas, must nevertheless vary considerably. 

 At the present moment, the rivers flowing from different 

 latitudes into the existing seas, must necessarily be pro- 

 ducing in the same marine basin accumulations of a very 

 dissimilar character ; and the distribution of the detritus, 

 must be greatly modified by the agency of those powerful 

 currents, to which allusion has already been made (p. 70). 

 These elements of variation in the deposits that may be 

 formed contemporaneously within the same ocean bed, 

 serve to explain the origin of similar discrepancies in the 

 contents of the ancient seas. Thus the same system, or 

 formation, may consist of strata containing exclusively 

 marine shells, corals, fishes, &c. intercalated with layers 

 of clays and sands, abounding in lacustrine shells, and 

 plants, and the remains of terrestrial animals and vegetables: 

 the former being strictly of marine, and the latter of Jluvio- 

 marine origin; in other words, consisting of deposits brought 

 into the sea by river currents loaded with the detritus of 

 the land. 



