Meteoric Stone toliicli fell at the Mission Station of St. Mark's. 7 



the drift-effect and the somewhat different lustre, the crust is very 

 similar ; both are alike covered with unusually shallow thumb- 

 marks, all showing differences so trifling in shape, depth, and distri- 

 bution that only on the most minute examination can they be 

 noticed. There are wanting, too, most of the criteria which other- 

 wise in the case of oriented meteorites, apart from the drift, lead 

 to the conclusion that the circumstances which determine the for- 

 mation of the surface are essentially different in front of and behind 

 the body moving through the atmosphere." From the complete 

 absence of trough-shaped cavities and deeply sunk hollows and 

 furrows, I think I am at liberty to draw the conclusion that the 

 existing superficial impressions are not to be referred to the action 

 of strongly compressed, incandescent gases having a rotatory motion, 

 since they are bound to have a quite different effect on the front and 

 on the back and, especially in the case of the latter, cannot affect 

 the whole surface so uniformly.! I might compare the hollows 

 with the scars which are occasionally formed by the scaling off of 

 small flat sherds in the baking of pottery, and attribute them solely 

 to the tension which must result from the considerable differences 

 of temperature between the cold interior of the meteorite and the 

 surface so highly heated immediately on its entering the atmosphere. 

 The existing insignificant distinctions can be explained by the fact 

 that in the forward part the difference between the temperature of 

 the surface and that of the interior is greater than at the back. On 

 the other hand, the extraordinary resemblance in size, shape, and 

 distribution of the impressions on both surfaces may be attributed 

 to the fact that the grain, texture, and mineralogical composition of 

 the St. Mark's stone are unusually uniform throughout, and that 

 in consequence there was nowhere a weak point favourable to the 

 attack of the forces which were transforming the surface ; the absence 

 of larger quantities of iron pyrites and nickel iron might, in par- 

 ticular, contribute to this. The scaling off of the sherds must 

 have taken place immediately after the meteorite had entered the 

 atmosphere, since the broken surfaces show the same crust as 

 the remaining parts of the surface. 



If the above considerations are correct, we must come to the con- 

 clusion that the structure and composition of the meteoric stone may 

 have a greater influence upon the contour of the surfaces than has 



* V. E. Cohen, I.e., Heft ii., 151-160. 



t V. E. Mach and P. Salcher, " Photographisehe Fixirung der durch Projectile 

 in der Luft eingeleiteten Vorgange." Sitz.-Ber. Ak, Wiss. Wien, 1887, xcv., ii., 

 764-780, 



