Raymond. — Correlation of the Ordovician Strata. 



PLATE 4. 



Fig. 1. An exposure of the lower beds of the Ordovician (Walchow and 

 Packerort formations) on the Lawa at Wassilkowa. The top of 

 the Lower Cambrian is at water-level; the Obolus sandstone, the 

 Dictyonema shale, and the Glauconitic sandstone all occur in the 

 fifteen feet of strata beneath the projecting beds seen in the middle 

 of the figure. The conspicuous beds are the lowest limestone 

 and belong to the zone of Megalaspis 'planilimhata (Bna). Above 

 this are seen the softer strata of Bn/s, then the harder limestone 

 of Buy, and at the top, the zone of Asaphus expansus, or Bus 

 (Bin a of Lamansky). 



Fig. 2. Quarry in the upper part of the Walchow and the lower part of the 

 Kunda at Putilowa. Both these localities are south of Lake 

 Ladoga and east of Petrograd, Russia. 



