610 A. W. GRABAU LOWER ORDOVICIC FORMATIONS 



these by shales with Asaphus expansus (3 c (3), above which lie in turn 

 the Gigas and Platyurus beds (3 c y) with Megalaspis gigas and Asaphus 

 platyurus. The succession is thus as in Dalarne, with the hiatus between 

 the Limbata and Expansus horizons, the chief difference being the replace- 

 ment of the Planilimbata limestone by Phyllograptus shale and the greater 

 development of the Ceratopyge beds. 



ORDOVICIC. OF CELAND 



This island, situated off the southeastern coast of Sweden, shows cer- 

 tain significant sections which are corroborative of the correctness of the 

 general thesis so far developed. The Cambric, well developed in its 

 middle facies, is disconformably succeeded by the Oboius conglomerate, 

 which rests on successively lower members of the Middle Cambric from 

 south to north. This conglomerate contains angular fragments of the 

 underlying Cambric beds, those in the northern region carrying the re- 

 mains of Paradoxides tessini. The cement of the conglomerate contains 

 Dictyonema flabelliforme, Obolus cf. apollinus, Oienus sp. Agnostus pisi- 

 formis and var. obesus. The Dictyonema is found only in the cement of 

 the upper part of the conglomerate, which is generally succeeded con- 

 formably by Dictyonema shale, except where this species occurs in the 

 cement of the conglomerate. This suggests that the two formations arc 

 more or less contemporaneous, the Obolus belonging to the eastern fauna 

 and the Dictyonema to the western. 



The Ceratopyge limestone rests conformably on the Dictyonema shale 

 when this is present, its base, as at Ottenby, on the south end of the 

 island, being sometimes represented by an alum shale (Ceratopyge shale) 

 carrying Shumardia pusilla Sars. and Ceratopyge forficula Sars., similar 

 to the Christiania development. The Ceratopyge limestone is succeeded 

 conformabty by the Planilimbata and Limbata limestones with their char- 

 acteristic fossils as elsewhere developed. This in turn is succeeded by 

 the Asaphus limestone, which is divided into a lower and an upper bed, 

 separated by a zone of limestone crowded with the globular cystoid 

 Sphceronis (Holocystites) pomum Gyllenh. The lower bed seems to be 

 identical with the Asaphus limestone of the mainland, but Asaphus ex- 

 pansus has not been found in it. It contains, however, Strophomena 

 jentschi Gagel at several places in northern (Eland. In the same rock 

 Holm is reported to have found a specimen of Didymograptus (Iso- 

 graptus) gibberulus (I. caduceus Salter). This is an Arenig species, 

 while Strophomena jentschi suggests Upper Ordovicic affinities. If the 

 latter is correct, then the break in the series comes here, as elsewhere in 

 Sweden, above the M. limbata limestone, the next succeeding bed being 



