Rejjorts and Proceedings — Geological Society of London. 91 



for a classification of igneous rocks which shall be natural and so 

 independent of all hypotheses, many will doubt whether such a 

 system is yet possible. Any well-established facts connecting 

 particular types of rocks with special modes of occurrence, depths of 

 consolidation, or even succession in geological time or restriction 

 within ' petrographical provinces,' might well claim to be taken into 

 account in a natural classification ; but are geologists agreed on any 

 of these points? M. Michel Levy replies in the negative. The 

 Wernerian heresy, from which the German petrologists have not yet 

 fully recovered, had it been true, would have afforded an impregnable 

 system of classification. Other systems, such as von Eichthofen's 

 ' natural classification of volcanic rocks,' have been founded on a 

 similar assumed generality of a local succession. If future researches 

 should bring to light general principles which will stand the test 

 of particular applications, petrology will certainly be placed on 

 a more philosophical footing. Meanwhile a classification like that 

 of our author, founded on mineralogical and structural characters, 

 the ultimate causes of which are only vaguely foreshadowed, cannot, 

 however useful, claim to be a natural one. 



The author is of opinion that the mode of occurrence of eruptive 

 rocks is not sufficiently closely connected with their structure to be 

 taken into account in a rational classification ; but when he attacks 

 the current division between plutonic and volcanic rocks, his position 

 is seriously weakened by his admission that such a grouping agrees 

 in the main with his own, founded on purely structural characters. 

 Again, the intermediate class of ' dyke-rocks,' to which he also 

 objects, appears in practice to be a very convenient one. Whether 

 its limits, as defined by Rosenbusch, are well chosen, is a different 

 question. Doubtless some geologists would prefer to include in it 

 the diabases, which, as structurally distinguished from the dolerites, 

 are characteristically found in dykes, sills, and small laccolites : 

 others, with M. Michel Levy, would exclude some of the so-called 

 acid ganggesteine. 



Our author expresses a hope that his somewhat bizarre symbolic 

 notation may serve to bridge over the gap pending a unification of 

 petrological nomenclature ; but it appears a little complex and very 

 likely to suffer in hasty writing, and it may be doubted whether it 

 will commend itself to the geologist any more than to the printer. 

 In the tabular exposition of the classification of Fouque and Levy, 

 however, it gives a degree of pi-ecision which would not otherwise 

 be attainable without lengthy descriptions. A. H. 



RBPOBTS .A-JSTZD PBOCBEDIUGS. 



Geological Society of London. 



I.— Dec. 18, 1889.— W. T. Blanford, L.L.D., F.R.S., President, in 

 the Chair. — The following communications were read : — 



1. " On the Occurrence of the Genus GirvaneUa, and remarks on 

 Oolitic Structure," By E. Wethered, Esq., F.G.S. 



The author referred to his previous work, wherein he had shown 



