ELECTRICAL PHENOMENA 73 



Champlain (Hallock), etc. Fulgurites in sand have been frequently 

 described. These have been found in the sands of the Libyan desert 

 (Gumbel), as well as in the sand and soil of moist climates. In 

 Silesia, near Olkusz, 26 tubes were found in an area of 200 by 100 

 feet, most of them associated in groups. In Cumberland, England, 

 near Drigg, fulgurites of exceptional size were found. Three of 

 these tubes were found in a sand hillock within an area of fifteen 

 square yards. One of them was traced perpendicularly to a depth of 

 40 feet, the basal part being much contorted and branched, owing to 

 the presence of many small pebbles in the soil. The maximum 

 diameter of this tube was 2^ inches. 



The finer structure of the glass lining of the tube has been espe- 

 cially investigated by Julien (53). He finds that the bubbles which 

 occur in such large numbers in the clear amorphous glass of the 

 tube contain no water, these bubbles probably bemg formed by the 

 expansion of heated air. The vesicles are elongated, and their 

 longer axes disposed radially. All sand grains within a radius of 

 a few millimeters were suddenly and completely fused. The inner 

 wall is practically free from bubbles, and is a clear, shining glass, 

 streaked and spotted with black and brown, according to the abun- 

 dance of iron-bearing minerals. Externally the form is very rough, 

 corrugated longitudinally and coated with partially fused sand 

 grains. The outline is an irregularly branching one, due to the 

 forking of the electric spark. The thickness of the wall varies from 

 0.1 cm. or less to 0.5 cm. or more, and the vesicles from less than 

 0.002 mm. to 1.2 mm. or over. The cross section is often nearly 

 circular ; at other times it is irregular. Sometimes the round hole is 

 merely lined by a network of fused materials. 



Of exceptional interest is a fulgurite described by Barrows (5) 

 from the Raritan sands of New Jersey. It was found in a mass of 

 sand fifty feet thick, resting on the South Amboy fire clay, and oc- 

 curred 15 to 20 feet above the clay or from 45 to 55 feet from the 

 surface formed by the Pensauken outwash gravels of Pleistocenic 

 age. The fulgurite ran at a low angle to the horizontal for about 

 15 feet parallel to the face of the bank. The length was about 19 

 feet, including branches, and the diameter of the tube varied from 

 3.2 cm. to 0.3 cm. The position of this tube suggests that it was 

 formed after part of the sand had been deposited and before the 

 laying down of the upper part of the sand. If this is the case, these 

 sands would have to be regarded as dune sands, since fulgurites will 

 form only in comparatively dry media. This interpretation is not 

 inconsistent with the character of the formation as a whole, which 

 is of continental rather than of marine origin. Of course the tube 



