114 ABRIDGEMENT OF THE STRATA. 



ficial beds of sand, loam, and gravel', are denominated modern 

 alluvium; and, as these last in some districts are strewed 

 with boulders and masses of primary rock, such deposits 

 with some others are termed ancient alluvium ; the beds of 

 gravel, &c., being supposed to be the result of agencies still 

 in operation, while the drift and boulders are regarded as 

 the effect of violent floods or inundations which have ceased 

 to act on our globe. These subjects of drift, or till, as it is 

 locally termed, and erratic blocks or boulders, have recently 

 engaged considerable attention, and an opinion is fast 

 gaining ground that the erratic substances in question are 

 the results of an agent now in operation, and that they 

 have been transported by icebergs which, on melting, have 

 deposited them at the bottom of the then existing sea. 

 M. Agassiz has suggested the glacial theory, to account for 

 these deposits ; but this hypothesis is scarcely received with 

 so much favour as the preceding ; while, in either case, the 

 introduction of ice, as a moving power, constitutes a new 

 and striking feature in geological inquiry. 



AEKANGEMENT OF THE STEATA. 



FOSSILIFEROUS DEPOSITS. 



The following table will convey a general idea of the 

 various formations, as regards their distinctive features of 

 succession, mineral composition, and fossil remains : 



I. Alluvium, modern and ancient ; the term modern being 

 applied to the deposits now in course of formation, or apper- 

 taining to the historic period, comprising beds of rivers, 

 lakes, peat-bogs, coral-limestones, volcanic ejections, calca- 

 reous deposits from mmeral springs, &c., containing the 

 remains and the works of man; the term ancient being 

 usually bestowed on like accumulations formed prior to 

 the historic era, and containing no vestiges of the human 

 race. 



