QIBB — A CHAPTER ON FOSSIL LIGHTNING. 
201 
the surface, wliich were vitrified and glassy in tlieir interior, and the 
chalk itself affected for a short distance around them. They were 
quite or nearly straight; in size, from half an inch to an inch in 
diameter, and were exposed in a fissure of the chalk. About three 
feet of these tubes were visible, and then they became lost. 
The finest examples of these lightning-tubes which have come under 
my notice in the London museums are those from Drigg, in Cumber- 
land, in the Museum of the Geological Society, and which have been 
described iu that Society's Transactions. They appear to be the most 
perfect, although larger tubes have been found at Natal. In speaking 
of these I shall combine a general description of the whole. 
It is in banks, hillocks, or mounds of loose sand, that they are gene- 
rally met with, sometimes, however, in immense hollows, or occa- 
sionally on declivities of mounds of sand. At Drig^ they were 
discovered in the middle of sand-banks forty feet high, between the 
river Irt and the sea, but projecting above the surface from the drifting 
away of the sand. These sand-banks are exceeded both in extent and 
height by those at Eskmeols, in the same county. On the shores of 
La Plata, in South America, Mr. Darwin found them in the sand- 
hillocks of Moldonado, which were constantly changing their position 
from not being protected by vegetation. This circumstance caused 
them to be found projecting above the surface, as at Drigg, and Mr. 
Darwin iuferred, from finding numerous fragments lying about, that 
they had at one time been buried at a greater depth.* These 
occurred in a level area of shifting sand, situated among some high 
sand-hillocks, distant about half a mile from a chain of hills 400 and 
500 feet high. In the Senne, Westphalia, similar tubes were found 
on the declivities of mounds of sand thirty feet high ; but occasionally 
some were noticed in cavities, described as hollowed out in the heath 
in the form of great bowls, 200 feet in circumference, with a depth of 
from twelve to fifteen feet. 
The position in which these tubes are found is one of some interest 
and importance. As usually encoimtered, they run vertically into 
the sand, at a varying depth. On the banks of La Plata four sets 
entered the sand perpendicularly, and one was traced 5^ feet into the 
* Darwin's Journal, vol. iii. 1839, p. 69. 
