324 Rev. A. Irving — The Permian- Trias Question. 



Germany is simply overwhelming. In the light of such evidence 

 the title and scope of Geinitz's great work on the Dyas is ftilly 

 justified ; and one can afford to let pass without further notice such 

 a condemnation of Geinitz's action as Prof. Roemer of Breslau 

 gave utterance to last year, when the subject was discussed in 

 Section C. of the British Association. 



All that I have seen in Middle Germany, both in Museums and in 

 open sections in the field, shows me that there is an unconformity 

 on a grand scale between the Trias and the Dyas, and also an 

 unconformity (on a smaller scale) between the lowest Bunter 

 strata and the Zechstein. This unconformity perhaps many members 

 of the Survey, whose notions of unconformity seem limited to the 

 particular form or kind of unconformity which is described in Prof. 

 Eamsay's Lectures on the Physical Geology of Great Britain,^ would 

 not be prepared to recognize. There, is however, another kind of 

 unconformity, which is quite a distinct thing from "contemporaneous 

 erosion and filling up " (a term first used by the late Prof. Jukes), 

 which is well described and illustrated in Geikie's edition of Jukes' 

 ]\Ianual of Geology, and is recognized in the later text-books of 

 Prof. Green and Prof. Geikie, In such cases erosion and partial 

 destruction of one set of beds has gone on to a considerable extent, 

 and the hollows formed by such erosion (whether aqueous or sub- 

 aerial) have been filled up by subsequent deposits without any 

 general divergence of dip of the two series of beds. Yet in such 

 a case the terms of Prof. Jukes' definition of unconformity,^ as 

 including every case in which " the base of one set of beds rests in 

 different places on different parts of another set of beds," are com- 

 plied with. Of course, in places where the erosion of the lower set 

 of beds is less pronounced (and the causes of inequality of erosion 

 are too obvious to need mention here), there may be an apparent con- 

 formity ; and so insufficiency of observation may mislead an observer 

 whose opportunities of observation are limited. This is no doubt 

 partly the cause of the error into which Murchison fell, when he 

 insisted repeatedly upon a conformity between the Zechstein and the 

 Bunter-Schiefer, In places, again, where an open section has been 

 considerably weathered, it often happens that, if the upper set of 

 beds is composed of friable material, the junction may be obscured 

 by the mere washing down of material by rain ; and this may 

 perhaps have been the case in places in which Murchison speaks of 

 a petrological transition from the Zechstein into the Bunterschiefer. 

 Sections however, which are fresh and open, and about the reading 

 of which there can be no mistake, are much more numerous in 

 Central Germany than they were thirty years ago ; and in no section 

 that I have seen has there been anything like a petrological 

 transition from the Zechstein into the Bunterschiefer, where the 

 junction was exposed. Breccias composed of fragments of the 

 underlying Upper Zechstein, and even in some cases of the Middle 

 Zechstein strata, are common enough. I have seen cases, in which 



1 5th edition, p. 36. 



2 Geikie's edition of Jukes' Manual, p. 230. 



