RAYMOND: CORRELATIOX OF THE ORDOVICIAX STRATA. 225 



the Orthoceras limestone is thickest, as on Oeland or at Kinnekulle, 

 Asaphus expansus, the guide fossil of the " Expansusschicht" is absent; 

 and there is found, above the strata containing a fauna which includes 

 a part of the species usually found associated with Asaphus cxpansus, 

 a layer with such quantities of the cystid Sphaeronis pomum as to make 

 a veritable cystid reef. Xo such reef is seen where Asaphus cxpansus 

 is present, as in Ostergotland or the Christiania district. Both 

 Sphaeronis and Asaphus cxpansus are reported from Dalecarlia, but, 

 according to Tornquist the former species is exceedingly rare, and not 

 quite typical, and that district will probably not prove to be an excep- 

 tion to the general rule. 



Very little has been done toward working out the details of the 

 various sections in the Orthoceras limestone, so that the sections 

 at Kinnekulle and Oeland are really the only ones which can be com- 

 pared. On Oeland, one finds above the bed with Sphaeronis pomum 

 the Upper Asaphus limestone, with numerous undescribed trilobites. 

 Moberg states that this zone occurs nowhere else and it certainly is not 

 present at Kinnekulle, where a cephalopod fauna is found in the red 

 limestone above the Sphaeronis bed. This cephalopod fauna is that 

 normally found in the Gigas limestone, and it seems that there is in 

 the Oeland section a zone which is lacking at Kinnekulle. Whether 

 ^he absence of Asaphus cxpansus from the thick sections is explainable 

 by the predominance of red sediments, or whether the Expansus beds 

 are actually absent is not at present apparent. It should be observed 

 that the extra thickness in these great sections is largely accounted 

 for by the unusual development of the Planilimbata limestone, though 

 of course the added zones above the Gigas limestone have something 

 to do with it. 



In Oeland, at Kinnekulle, and in Delarne, one finds considerable 

 limestone above the Gigas limestone, which by the Swedish geologists 

 is included in the Orthoceras limestone. This limestone contains 

 three faunal zones, according to the Swedish geologists, but the faunas 

 of the three seem very much alike. The lower zone contains Asaphus 

 platyurus and Echinosphacrites aurantium, fossils found in Ci^ of 

 Russia, and lUacnus chiron is found in Ci,3 of that country, but the 

 other guide fossils are mostly species not found in Russia. The pres- 

 ence of Didymogr aphis geminus in the middle zone of the three in 

 Oeland is noteworthy, for it serves to complete the parallelization of 

 the Scanian and Oeland sections. 



The presence of Ogygiocaris, which seems to have an exceedingly 

 narrow vertical range, in the Xemagraptus zone in Jemtland and in the 



