SG DE. L. F. SPAi'H OX THE AMMONITES [vol. lxxix. 



oxygen, and poisoned by hydrogen sulphide. 1 In such bituminous 

 shales, only nee tonic or pelagic forms of ammonites would be 

 expected to occur. Now, in the Suabian Posidonomya Shales, 

 which Pompeckj 3 considered to be such a 'fossil Black Sea,' 

 Dactylioceras is throughout 3 by far the commonest ammonite, 

 although the probably pelagic PJiylloceras and Lytoceras and 

 nectonic Harpocerates are also numerous. The occurrence of beds 

 of maximum abundance, including ' nests ' of immature ammonites, 

 alternating with la\ r ers in which these fossils are rare, then the 

 occurrence of nodules or limestone-bands in places in the succession 

 make it probable, of course, that in an enormously long interval 

 of geological time, conditions like those in the Black Sea were not 

 continuously persistent. I would assume a ' Nautiloid ' mode of 

 life for both Dactylioceras and at least those Arietidae that had 

 not developed a smooth, symmetrical, oxycone shell. 



On the east, of course, the Liassic sea terminated against an 

 old land of Pabeozoic rocks, uoav underlying the London Basin, 

 and continuous with the Ardenno-Rhenanian isle farther east. 

 A. de Lapparent 4 and P. Lemoine 5 traced the southern shore-line 

 of this land from Dorset by way of Normandy, where the Lower 

 Lias apparently has not yet been zoned in detail, across to the 

 Ardennes, and Oppel 6 before them stated that his Suabian 

 tiiberculatus bed agreed, both mineralogically and palaeontologi- 

 eally, with that of Avallon (Yonne). From the identity of the 

 micro-fauna of Wurtemberg with that of France, and the fact 

 that the whole of the Lias a, in all its horizons, shows a similarity 

 with that of France, increasing the farther one departs from the 

 eastern and littoral facies of the Suabian Lias, Issler concludes 7 

 that the Black Forest and the Vosges were covered by the sea. If 

 so, there was a continuous sea from Suabia to Dorset on the one 

 hand, and by way of Franconia and Prussia to Lincolnshire on the 

 other ; for the Scunthorpe Ironstone shows great resemblance to 

 the Harzburg Ironstone of North Germany. Issler also assumes 

 that in Wurtemberg the tuherculatus bed and succeeding oil- 

 shale indicate a retreat of the sea, already begun in Upper Goroni- 

 ceras times, and the formation of quiet bays of the sea, with 

 abundant crinoids. It may be noted, however, that the appearance 

 of cryptogenous elements preceded that renewed inrush of the sea 

 which brought about the change of facies represented by Lias /3. 



1 J. F. Pompeckj, ' Geologische Einfliisse auf die Geschichte des Lebens ' 

 Sitz. Ber. Preuss. Akad. Wissensch. vol. xxxiii (1920) p. 686. 



2 ' Das Meer des Kupferschief ers ' Branca Festschrift, Leipzig, 1914, p. 481. 

 :i B. Hauff, ' Untersuchung der Fossilfundstatten von Holzmaden, &c.' 



Palfeontographica, vol. lxiv (1921) p. 24. 



* ' Traite de Geologie ' 5th ed. (1906) vol. ii, p. 1117. 



5 ' GJologie du Bassin de Paris' 1911, p. 83. 



c ' Die Juraformation Englands, Frankreichs & des S.W. Deutschlands ' 

 Wiirtt. Naturwissensch. Jahresh. vol. xii (1856) p. 167. 



7 ' Beitrage zur Stratigraphie & Mikrofauna des Lias in Schwaben ' Palse- 

 ontographica, vol. lv (1908) pp. 19 & 20. 



