138 
THE GEOLOGIST. 
In various papers in the " Edinburgh New Philosophical Journal" 
(new series, vol. iii. p. 112 ; iv. p. 317 ; v. p. 275 ; and vii. p. 226) 
I have explained many of my deductions, and I have shown that 
many peculiarities of physical geography at former epochs may be 
learned from a knowledge of the directions of the currents in various 
localities. In those papers I entered into some portions of the sub- 
ject at greater length than would be proper on the present occasion, 
when I shall attempt to give a general popular outline of the whole, 
referring the reader to those papers for more special information. 
I have often felt surprised that scarcely anyone has entered into this 
field of inquiry, in which the facts are so marked and distinct. If 
the current structures had been on a small scale requiring the aid of 
a microscope, there would have been good i-easou for this ; but such 
is not the case ; although T find that, from some extraordinary mis- 
understanding, many persons have imagined that it is so. Unassisted 
eyes and a compass are all that are requisite in determining the 
greater number of the facts, and I have never before said that the 
microscope is not required ,because I never thought anyone would 
imagine that it was. Moreover, many of the structures have been 
known long enough, for they are of such a character that no one could 
overlook them, although sufficient attention may not have been paid 
to their teachings ; and the study of their relation to one another 
and to other facts in an accurate and business-like manner may have 
been neglected. 
If advantage be taken of an artificial water-course, or of natural 
streams of water, to examine the effect of the current in the deposition 
of sand, it is easy to see that, according to the circumstances of the 
case, three very different kinds of structure are formed, from which 
the direction of the currents could easily be ascertained. If the 
bottom be tolerably level, and the velocity of the current just suffi- 
cient to drift forward particles of sand, a kind of grained or striped 
surface is almost always produced. The variable motion of the water 
along a particular line marks that line on the surface of the sand, in 
elongated patches of various colour and character, so distinctly that, 
even when the current has ceased, or the water has been dried up, 
we can clearly perceive the direction in which the curi-ent moved. 
If some of the sand thus drifted forward accumulate at the bottom, 
