RAYMOND: CORRELATION OF THE ORDOVICIAN STRATA. 221 



occur between the limestone strata of the Orthoceras limestone, the 

 species found being Tetragraptus bigshyi Hall, Didymograptus eztensvs 

 Hall, and PhyUograptus cor Strandmark. 



The fossils of the Lower Didymograptus shales have been described 

 by Tornquist (S3). These shales are much better developed in south- 

 eastern Scania than about Lund. 



The zone of Isograptus gihhcndus contains Isograptus gihhcrulus 

 Nich., Didymograptus extensiis Hall, D. patulus Hall, and D. mobcrgi 

 Tqst. 



The zone of PhyUograptus angustifolius has Didymograptus prae- 

 nuntius Tqst., PhyUograptus angustifolius Hall, and Tetragraptus 

 pendens praesagus Tqst. i 



The zone with Didymograptus haUicns has a larger fauna, among the 

 species being Didymograptus constrictus Hall, D. balticus Tullb., 

 Tetragraptus quadribrachiatus Hall, Dicliograptus octobrachiatus Hall, 

 and Clonograptus suhtilis Tqst. 



The lowest zone contains Tetragraptus phyUograptoides Linrs., T. 

 approximatus Xich., T. scrra (Brong.), Didymograptus undulatus Tqst., 

 and D. hohni Tqst. 



The Ceratopyge zone is poorly developed in Scania, but both the 

 Ceratopyge limestone and Shumardia shale have been shown to be 

 present, with the usual fossils. 



The Dictyonema shales are subdivided into three zones. 



C, zone with Bryograptus kjerulfi and Dictyonema norvegica. 



B, zone with Clonograptus teneUus in four varieties. 



A, zone of Dictyonema flabeUiforme in which, interstratified with 

 shales, are beds of limestone with Hystcrolenus tdrnquisti and H. 

 levicaudus. 



Very little seems to be known of the thicknesses of strata in Scania. 

 On seeing the outcrops in the field, one receives the impression thai; 

 they are very small. In a boring made at Stabbarp, northeast of Lund, 

 the Chasmops beds were encountered between eighty-six and ninety- 

 two meters below the surface and shales of the PhyUograptus cf. typus 

 zone at a depth of 102 meters, thus indicating a thickness of about ten 

 meters for the Lower Dicellograptus shales. 



At Jerrestad in eastern Scania Olin measured a section 425 cm. in 

 thickness, all in the Trinucleus zone, and most sections which it is 

 possible to measure are of this order or of less thickness. 



