FULGURITES FROM WISCONSIN 141 



A NOTE OX FULGURITES FROM SPARTA. WISCONSIN 



W. D. SHIPTOX. 



During the summer of 1915 some fulgurites were found near 

 Sparta. Wisconsin, in a small sand knoll composed of residual 

 quartz grains of the Potsdam formation, which is Upper Cam- 

 brian in age. The sand is fairly clean and of uniform char- 

 acter and is being reworked continually by the wind since there 

 is only a scant covering of vegetation. 



The fulgurites consist of irregular, thin-walled tubes of fused 

 siliceous sand grains. The tubes vary in length and diameter. 

 The smallest are about one-eighth inch long while the largest are 

 several inches in length. The pieces may be the fragments of 

 one large tube, the smaller pieces being the branches from the 

 main stem. The surfaces of the fulgurites are very irregular 

 and are traversed by deep furrows with minor undulations. 

 The entire surface is covered with the grains of sand which 

 came in contact with the fused material. Some of the grains 

 are white and opaque, due to complete fusion, while others are 

 brown and have remained unaltered. The interior of the ful- 

 gurites is smooth, highly glazed glass and the surfaces corres- 

 pond to the furrowed surfaces of the outer walls in outline. 

 The deviations of the tubes from a circular form are due prob- 

 ably to the pressure of the adjacent sand while the fulgurites 

 were still in a fused condition. 



Fulgurites are caused by lightning striking in sand and fus 

 ing the siliceous sand grains into a tubular form. 



