Vol. 50.] GOSAD" BEDS OF THE GOSAU DISTRICT. 137 



IV. Geological Horizon of the Gosau Beds. 



This question can be considered from two aspects : (a) strati- 

 graphically, and (o) palseontologically. 



(a). As we have already seen, the Gosau Beds almost everywhere 

 rest with a marked unconformity upon the older Alpine Triassic 

 and Bhsetic limestones, and only at one locality do they rest on 

 older Cretaceous beds. However, the section at Urschlauer Achen, 

 near Salzburg, which I refer to, establishes the fact that the Gosau 

 Beds are younger than the Gault. The Gosau fossils from this locality 

 occur, according to Dr. Oppel, 1 in a dark marl, which is overlain by 

 Orbitulitenkalk, and rests on Neocomienmergel with Orioceras ; 

 this in turn rests on Kimmeridgekalke. Sedgwick and Murchison 

 supposed that the lowest Hippurite-limestone rested unconformably 

 on the older Alpine limestone, and that the Gosau Beds overlay un- 

 conformably the Hippurite-limestone ; but it has since been conclu- 

 sively shown that the coarse basement-conglomerate comes below 

 the Hippurite-limestone, and appearances only can be said to lend 

 any support to the view that the conspicuous banks of Hippurite- 

 limestone rest immediately against the older Triassic rocks, and that 

 the rest of the Gosau series does not follow them in conformable 

 sequence. Also the Gosau Beds are never seen to pass upward into 

 any younger formation. Sedgwick and Murchison supposed that 

 the unfossiliferous sandy marls, sandstones, and grits at the top of 

 the Gosau series of the Gosauthal were of Tertiary age, 2 while on 

 palaeontological grounds they believed that the fossiliferous series 

 represented passage-beds between the Upper Chalk and the Lower 

 Eocene. But we shall see from palaeontological considerations that 

 the fossiliferous series cannot represent such passage-beds. It 

 passes up imperceptibly into the unfossiliferous group, and there is 

 a very gradual dying out of molluscan remains, so that no definite 

 line of demarcation can be drawn between them. The majority of 

 authors who have written on the subject decidedly agree in regarding 

 the Gosau Beds as constituting one complete formation, which is 

 singularly isolated stratigraphically. We shall find that more im- 

 portant results will follow from considering the question of the 

 geological horizon. 



(b). In doing so, it may be as well, first of all, to summarize the 

 opinions of the various authors who have expressed views on 

 palaeontological grounds as to the age of the Gosau Beds. 



Ami Boue studied the Gosau Beds in the neighbourhood of 

 Griinbach, Neue Welt, in 1822. He took them at first for Jurassic, 

 but subsequently changed his opinion in 1824, and correlated them 

 with the Greensand or Quadersandstein. 3 Keferstein 4 included the 



1 Zittel, Denkschrift. d. kaiserl. Akad. Wissensch. Wien, vol. xxv. (1866) pt. ii. 

 p. 162. 



2 Trans. Geol. Soc. ser. 2, vol. iii. pt. ii. (1832) p. 359. 



3 See Zittel, op. supra tit. p. 174. 



4 ' Geologie von Teutschland,' vol. v. 1827. 



Q. J. G. S. No. 198. l 



