140 



THE GEOLOGIST. 



must be so much less than above a h that the saud can be left at b c, 

 and not drifted forward beyond c. When such is the relative velocity 

 of the current before and after arriving at b, the particles of sand are 

 drifted along the bottom from a to h, and thrown down on the slope 

 6 c at an angle of from 30° to 40°, varying according to the character 

 of the material. We may often see beds of this kind in the process 

 of being formed in rivers and water-courses, and can clearly perceive 

 that the current must come fi'om the opposite quarter to that towards 

 which the beds parallel to b c dip. When the water is all dried up, 

 and especially in frosty weather, when the otherwise loose sand is con- 

 solidated with ice, it is easy, by cutting into small beds of this kind 

 of structure, to see the smaller bands of varying colour and character 

 parallel to b c, represented by the lines in fig. 1, and to perceive that 

 it is identical with much of the so-called " false-bedding." Since, 

 however, some false-bedding has been produced in a very different 

 manner, it is desirable to distinguish that just described by a special 

 name, and I have therefore employed the term " drift-bedding," in 

 allusion to its being formed by the drifting forward of the material, 

 and to its being so pre-eminently characteristic of deposits drifted 

 into their present resting-places, and not in anywise deposited from 

 above, as in the case of other kinds of stratification. False stratifi- 

 cation may also have been produced under a variety of circumstances, 

 differing from those just described ; but in many cases, as when, for 

 instance, a single bed, as in fig. 1, extends with uniform thickness and 

 character for several hundred yards, all other explanations are out of 

 question. 



Strictly speaking, perfectly developed di'ift-bedding and simple 

 horizontal stratification are two extreme structures which gradually 

 pass into each other. In drift-bedding the material is drifted forward 

 aloug the bottom a b, and thrown down on b c, whilst none is 

 deposited on a 6 or c e. On the contrary, where simple horizontal 

 stratification is formed, none is washed forward along the bottom, but 

 all is deposited from above, more or less uniformly, from a to e. The 

 connecting link between these is the " grained and striped stratifica- 

 tion." In passing into this, the angle bed becomes gradually less, 

 the velocity of the current above a b and c e becomes more and more 

 nearly equal, the sand is drifted over the fixce of the inclined plane b c, 



