202 THE GEOLOGIST. 



sand by Mr. Darwin ; but, as the diameter of the whole was nearly 

 equal, it must have extended to a greater depth. He found one 

 deviating from a right line at a considerable bend, amounting to 33°; 

 and from this tube two small branches about a foot apart were sent 

 off, one pointing downwards and the other upwards. This is an 

 illustration of the forked character of the electric fluid, which, besides 

 its division into two branches, would seem to have turned back in this 

 case at an acute angle of 26° to the line of its main course. At Drigg 

 many tubes were found dividing into two branches and pursuing a 

 tortuous course into the sand. Some of the tubes gave off several 

 small branches, the diameter of which was not a fifth of the tube 

 whence they sprang ; others, again, deviated almost at right angles, 

 glancing off, as it seemed, by the interruption of a pebble, as in the 

 example figured in the Geological Society's Transactions (vol. v. First 

 Series, pi. 3). 



It is looked upon as a fact somewhat remarkable, that quite a 

 number of tubes have been discovered to enter the surface of these 

 sand-hills in comparatively limited areas ; at least, such was the case 

 at Drigg, on the shores of La Plata, and also in Geimany. Mr„ 

 Darwin counted more than four within a space of sixty yards by 

 twenty. Three were noticed within an area of fifteen yards, upon 

 a single hillock at Drigg ; and the same number were found in an 

 equally limited space in Germany, as described by M. Ribbentrop. 

 In considering this peculiarity, Mr. Darwin believes in the improba- 

 bility of these tubes being produced by successive and distinct shocks 

 — an opiDion in which most persons will concur. Yet, whilst acknow- 

 ledging the possibility of a division of the lightning into separate 

 branches shortly before entering the ground, as suggested by him, I 

 still think that the electric fluid may have run along the surface of 

 the sand, and then entered it at different spots remotely situated 

 from one another. This view is by no means in-ational, when we 

 reflect upon the truly singular peculiarities associated with this won- 

 derful fluid, which may be seen at times to run along the surface of 

 bodies and suddenly disappear. The intensity of its action, too, is 

 oftentimes modified by the amount of resistance offered by substances 

 struck by it. On the other hand, the electric fluid may divide into 



