M. Haidingev on the Original Formation of Aerolites. 445 



a pulverulent aggregate of all the substances found in meteorites, 

 these could not be brought to crystallize gradually without some 

 means or source by which heat could subsequently act upon them; 

 and it maybe questionable how far the mutual pressure of masses, 

 or the attraction of a great whole on its isolated and still uncon- 

 nected particles, may possibly suffice to produce such an effect. 



T may here anticipate that a mere pulverulent aggregate having 

 a rotatory movement in space must necessarily also acquire a sphe- 

 roidal form dependent upon rotation, exactly like a liquid (accord- 

 ing to Professor Plateau's experiments) not acted on by terres- 

 trial attraction, and consequently in a state of free suspension. 



A septaria, an object familiar to mineralogists and geologists, 

 may serve to convey an idea of the effects of pressure acting from 

 the circumference to the centre. Septaria? are spheroidal tuberi- 

 form bodies, occasionally slightly compressed in one direction 

 (see fig 3), consisting of an external solid shell or crust of com- 

 pact argillaceous sphaerosiderite, filled up with the same sub- 

 stance, and intersected by numerous and somewhat imperfect 

 veins of calcareous and magnesio-calcareous spar. Fig 3 is an 

 autotype, taken from a specimen in the Imperial Museum of 



Fig. 3. 



Vienna. The formation of such a septaria may be explained as 

 follows : — within a stratum of clay, the particles richest in the 

 carbonate of oxide of iron agglomerate or coalesce : the clay- 



