294 J. W. JUDO ON THE ANCIENT VOLCANO OF 



and apparently inexplicable relations, or concerning the true inter- 

 pretation of the structure of which greater diversities of opinion 

 have existed among geologists. If, therefore, I venture on this 

 occasion to offer a new explanation of the phenomena of a district 

 which has already been so patiently and accurately studied and so 

 often described by able geologists, it is not in any spirit of presump- 

 tion, but rather from the conviction that what is necessary to the 

 more perfect elucidation of the singularly involved questions con- 

 cerning the age and relations of the different geological formations 

 of the district is the means of comparison with another area in which 

 the rock-masses are more perfectly exhibited. And such a key to 

 the right understanding of the often perplexing and sometimes 

 seemingly contradictory phenomena presented by the Hungarian 

 rocks, I hope to show in the present memoir, is afforded by those 

 districts of Scotland which furnish us with such singularly favour- 

 able opportunities for geological research. And if, as I hope to 

 make manifest in the sequel, harmony and simplicity are by this 

 explanation introduced where all before was complication and con- 

 fusion, the circumstance may be fairly claimed as an additional 

 confirmation of the truth of the solution offered. 



In treating this question it will be most convenient to present, 

 in the first place, a general sketch of the universally accepted facts 

 concerning the geological structure of the district in question, and, 

 in the second, to discuss the various interpretations which have been 

 offered with a view to explaining the origin of that structure. 



Part I. — SketcJi of the Geological Structure of tlie Schemnitz 

 District. 



The volcanic rocks of the Schemnitz district cover an area 

 about 50 miles in diameter. It will not be necessary for our pre- 

 sent purpose to notice in detail the various sedimentary formations 

 of more ancient date, through which these Tertiary volcanic masses 

 have been erupted, and upon which they are seen at many points to 

 be superimposed ; suffice it to remark that the rocks subjacent to 

 those igneous formations with which we are more particularly en- 

 gaged in the present memoir include many old granitic and meta- 

 m orphic masses, together with representatives of nearly the whole 

 series of fossiliferous strata, from the Trias to the Eocene Nummu- 

 litic inclusive — and that the whole succession of Secondary and older 

 Tertiary rocks in this district appears to have been continuously 

 deposited, and without any of those great breaks which are indi- 

 cated either by a sudden change in fauna or by wide-spread physi- 

 cal unconformity between them. 



The outer portion of the great tract of volcanic rocks which we are 

 here considering, constitutes a broad girdle consisting of lavas with 

 their associated agglomerates and tuffs ; these, reduced by denuda- 

 tion to a number of more or less isolated mountain-masses, from 

 3000 to 4000 feet above the sea, and almost everywhere covered by 

 dense forests, overlook the central depressed area in which lie the 



