138 THE GEOLOGIST. 



In various papers in the "Edinburgh New Philosophical Journal" 

 (new series, vol. iii. p. 112 ; iv. p. 317 ; v. p. 275 j 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 reason for this ; but such 

 is not the case ; although I 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 tlie current has ceased, or the water has been dried up, 

 we can clearly perceive the direction in which the current moved. 

 If some of the sand thus drifted forward accumulate at the bottom. 



