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which the current moved may be known, though not the 
direction from which it came ; but this can almost always be 
ascertained from the presence of the structures described 
below. If the current becomes somewhat more rapid, not 
only are ripples formed on the surface of the bottom, but the 
particles of sand are drifted forward, and thrown down in 
layers on that side of the ripples towards which the current 
moves. This structure is what I call " ripple drifted." 
When the current becomes more powerful, these waves 
increase in size, and pass into that structure which is gene- 
rally called "false bedding," where the separate thin beds are 
inclined at an angle of about 30° to the plane of true bed- 
ding. This I call "drift bedded;" and in it, as well as the 
much smaller variety, which I name " ripple drifted," the 
direction from which the current came, is the opposite to 
that of the dip of the detached thin beds, in relation to the 
plane of true bedding. 
When either of these structures is observed in progress in 
modern sand drifts, admirable examples of which, on a large 
scale, are to be seen at both ends of the Menai Strait, it will 
be perceived that the line of the dip of the talus is not con- 
stantly in the true direction of the current, on account of the 
formation of complicated deltoid deposits, in which the line of 
the dip of their sloping termination varies very considerably 
on each side of that of the current. Its mean direction, how- 
ever, coincides with it ; and, hence, if a number of properly 
placed observations be made, their mean gives a result very 
closely agreeing with the true line of the current. 
From one or other of these structures, then, the direction 
of the current which drifted onwards a bed of sandstone can 
almost always be ascertained ; and to illustrate the accuracy 
that can be attained, with proper precaution, I would men- 
tion that, in many cases, where I have observed it in quarries 
in the same bed of stone, at a short distance apart, the mean 
