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Arrangement of' Rocks. By Dr K. C. Von Leonhard, Pro- 

 fessor of Mineralogy and Geology, Heidelberg. Communi- 

 cated by the Author. 



The division of rocks into Primitive, Transition, and Second- 

 ary, does not answer the present state of science. In our opi- 

 nion, the regular or stratified rocks (norraale felsgebilde), may 

 with justice be separated into a series of more or less characteristic 

 groups. Certain analogies of character, a close connexion by 

 means of reciprocal gradation, organic remains, and finally a 

 constant, or at least a very frequent, appearance of various mem- 

 bers of such groups, allow us to regard them as more or less 

 well defined. The constant occurrence of one or more mem- 

 bers of the series, and being always in the same position, de- 

 cide as to the identity of the other members, thus affording light 

 in many ambiguous cases. The nature of organic remains is, 

 above all, of the greatest importance in the arrangement of 

 such groups of regular rocks. The groups I have adopted in 

 my system are the following : — 



I. Postdiluvial. 

 II. Diluvial. 



III, Fresh-water gypsum, with coarse limestone (grob 



kalk), and plastic clay. 



IV. Chalk and green sand. 



V. Jura and oolite limestone. 

 VI. Lias and keuper. 

 VII. Shell limestone (muschel kalk), and variegated sand- 

 stone. 

 VIII. Magnesian limestone (zechstein), and red sandstone 

 (Tod-liegendes). 

 XI. Coal. 

 X. Transition limestone, greywacke, and clay-slate. 



In judging of the relations of the absolute age of irregular 

 rocks (abnorme felsenmassen), we meet with many difficulties. 

 We want there the criterions that occur in the regular rocks, 

 and the relative age is itself a problem whose solution is not 

 admissible but within certain limits. 



