402 REV. A. IRVING ON THE DYAS (PERMIAN) 
and when we bear in mind the absence of the Zechstein (and there- 
fore of Dyassic marine conditions) in the country intervening between 
the Black-Forest region and the Bohemian region, and the prevalence 
there of ‘“ continental” conditions through all the periods of the 
Dyas and Trias (except during Muschelkalk times), we can under- 
stand, I think, the marked difference which presents itself between 
the more northerly Dyassic marine fauna (Zechstein) and the more 
southerly fauna of the Alpine Trias. Even where dry land was 
wanting in the intervening area, the waters which existed must 
have been so shallow and turbid (as is shown by the nature of their 
deposits) that living forms would for the most part recede from them 
to the north and the south, leaving only such remnants of a fauna 
as are represented by Palwoniscus vratislaviensis, Xenacanthus 
Dechen, and Acanthodes gracilis of the red limestones, which are 
here and there intercalated with the mechanical sedimentary 
deposits of the Rothliegende*. The fauna which remained in the 
northern area became, perhaps for reasons already suggested, stunted 
and dwarfed, while the number of species diminished. On the other 
hand, the more favourable conditions prevalent in the marine area 
to the south of the great barrier would cause these forms to continue 
and even to fiourish (with some modifications) long after animals of 
the same Paleozoic facies as themselves had disappeared altogether 
from the fauna of more northern seas. Migration of species caused 
by alterations in the relative levels of sea and land, with the acci- 
dental formation of barriers affecting oceanic circulation and there- 
fore the temperature of the waters, together with such modifications 
of growth as would be induced by a somewhat altered set of con- 
ditions in their environment, can be accounted for on considerations 
based upon the indications which we can read to-day of the past 
physical geography of Central Europe; and such considerations seem 
to furnish the explanation of what has been hitherto looked upon as 
an anomaly in the phenomena presented by a comparison of the 
post-Carboniferous fauna with the fauna of the Alpine Trias. 
Discussion. 
The Presrpenr pointed out that the name Permian was formed 
on a sound principle, and that the name Dyas was formed on a 
principle which was objectionable. 
Prof. T. Ruprerr Jones, thanking the author for his collection of 
facts and opinions, protested against a continuance of M. Marcou’s 
disrespectfully worded allusions to the late Sir R. I. Murchison’s 
mistakes, whether supposed or proved. Sir Roderick thought he 
had reason to complete his “ Permian System ” symmetrically with 
the Bunterschiefer. If an unconformity really occurs between the 
Zechstein and this sandstone, it need not destroy the systematic 
succession, and certainly need not be made an occasion to reiterate 
irreverent remarks on one who advanced geology very much many 
years ago. As for the name “ Permian,” it was not to be thrown 
away because other strata also occur in the Government of Perm, 
* Oredner, 742d. p..483. 
