RAYMOND: CORRELu\.TION OF THE ORDOVICIAN STRATA. 239 



3. Thin-bedded, pure, fine-grained limestone with Leper- 



ditia fab ulitcs. 21 o ^ 



2. ^Massive pure limestone and layers of black chert. 

 Maclurites magnu6', Tetradium syringoporoidcs, Ampyx 

 halli, and brachiopods. 200 ^ 



1. Massive and thin-bedded pure and magnesian limestone. 600=*= 



Beekmantown limestone. 

 Zones 1 to 3 are correlated with the Stones River. 



According to Dr. Ulrich, the section near Chambersburg, Pa., has 

 a " lower Echinosphaerites bed," forty to fifty feet in thickness, resting 

 upon about 150 feet of limestone referred by him to the LowA'ille 

 (4 of section on preceding page). This Echinosphaerites bed, which 

 lithologically is a very earthy limestone is said by Ulrich (119, p. 322) 

 to be overlain by about 300 feet of hard dark limestone with Nidulites, 

 and that in turn by 270 ^ feet of strata in which thin beds of lime- 

 stone are interstratified with thick beds of shale. These strata are 

 characterized by Christiania. A few feet below the top is the upper 

 Echinosphaerites zone, and here Christiania is most abundant. The 

 Christiania beds are capped by the Martinsburg shale, which con- 

 tains Triarthrus, Cryptolithus, and Corynoides. 



At Strasburg, Virginia, still according to Ulrich, the lower Echino- 

 sphaerites bed rests upon a cherty limestone 100 feet thick, and the 

 Echinosphaerites is accompanied by brachiopods and bryozoans which 

 suggest to him a correlation with the Decorah shale of Minnesota 

 (called Black River by Ulrich). Above this zone are the massive beds 

 with Nidulites, 207 feet thick, followed by a forty foot bed of argilla- 

 ceous gray limestone and calcareous shale, containing Echinosphaer- 

 ites (upper zone) and brachiopods, with other fossils characteristic 

 of the Christiania fauna. This bed is followed above by 300 feet of 

 thin-bedded argillaceous light gray limestone and calcareous shale, 

 passing at the top into true shales. This limestone is referred to the 

 Martinsburg, since it has, in shaly beds ten to thirty feet above the 

 base, Corynoides cf. C. gracilis, C. calicidaris, Climacograptus spinifer, 

 Leptobolus insignis, etc. 



This manner of occurrence is in striking accord with that in Xorw^ay, 

 where Echinosphaerites occurs first in stage 4a/S without Christiania, 

 and then at a higher horizon 4ba with that fossil. 



At Bellefonte, Penn., according to observations made by Mr. R. M. 



1 These figures are given on the authority of Ulrich and do not agree with the sections pub- 

 lished by Stose. 



