METEORITE CRATERS — SPENCER 325 



at Kimberley and the still larger Premier diamond mine near 

 Pretoria. 



A closer analogy is given by the craters formed by military 

 mines -" and high-explosive shells. The mine crater of La Boisselle, 

 on the Somme (fig. 3c, pi. 2), exploded on July 1, 1916, was 270 

 feet in diameter from rim to rim and TO feet deep. The rim con- 

 sisted of debris piled up to a height of 15 feet above ground level 

 and the outer slopes extended to 90 feet beyond, the total diameter 

 being 400 feet. In this mine two charges of 3G,000 and 24,000 

 pounds, laid at 60 feet apart and 52 feet deep, were fired together. 

 The positions of the two charges are shown on figure 3c by the 

 dotted squares. They formed a circular crater of greater depth 

 than the charges. One of the craters on Hill 60, near Ypres, was 

 340 feet across the rim, and 67 feet deep ; here there was one charge 

 of 70,000 pounds of ammonal. These dimensions are comparable 

 with those of the Henbury meteorite craters, but the craters here 

 were in much softer rocks — chalk at La Boisselle and Eocene sand 

 and clay at Hill 60. A photograph -^ of a devastated area on the 

 Aisne in France, showing numerous water-logged shell holes and 

 stripped trees, is extraordinarily similar to one of Dr. Kulik's photo- 

 graphs of the Siberian craters, only much more impressive (pi. 5). 



As examples of much smaller craters produced by artificial means 

 mention may be made of the splashes of drops -^ (also rain on mud 

 flats), clay balls thrown on a slab of clay, and shots on armor plates. 



Note added September 15, 193^/. — Since the above paper was written, a more 

 detailed investigation has been made of the materials from meteorite craters.'" 

 Further evidence is forthcoming that very high temperatures prevailed at the 

 time the craters were formed. The meteoric iron was vaporized in large 

 amount and condensed as minute spheres; those which fell into the boiling 

 silica were preserved. Some of the vesicular silica glass from Wabar is esti- 

 mated to contain as many as 2,000,000 of these minute polished spheres of 

 nickel-iron per cubic centimeter. 



» Military mining, worlv of tlie Royal Kngineers in the European War, 1914-10. Insti- 

 tution of Royal EnKinoors, Chatliam, 1922. 



"War Museum pliotograph no. Q378G1. 



=« Wortliington, II. M., The splash of a drop and allied phenomena. Proc. Roy. Inst. 

 Great Britain, vol. 14 (for 1894), pp. 289-303, 15 pis., 1895. Cole, R. S., The photog- 

 raphy of the splash of a drop. Nature, vol. 50, p. 222, 1894. Worthlngton, A. M., and 

 Cole, R. S., Impact with a li(iuld surface studied hy the aid of instantaneous photography. 

 I'hil. Trans. Roy. Soc, London, ser. A, vol. 189, jip. 137-148, 8 pis., 1897 ; vol. 194, pp. 

 175-199, 6 pis., 1900. Worthlngton, A. M., The splash of a drop. London, 1895 ; 

 A study of splashes. London, 1908. Numerous interesting photographs are given in 

 these booljs and papers, some of which bear a certain resemblance In form to meteorite 

 craters. 



» Spencer, L. J., Meteoric iron and silica-glass from the meteorite craters of Henbury 

 (Central Australia) and Wabar (Arabia). Mlueraloglcal Mag., vol. 23, pp. 387-404, 

 8 pis.. 1933. 



