TWENHOFEL: expedition to the BALTIC PROVINCES. 293 



To some of the divisions, geographical formational names were 

 applied by Schmidt, while others were named after some character- 

 istic fossil or lithic characteristic. Each division coming within the 

 writer's problem has been redefined, Schmidt's geographical terms 

 have been retained, with, so far as determinable, the limitations 

 imposed by him. To divisions named after characteristic fossils, 

 geographical formational names have been applied. 



The names of the fossils listed have been taken from Schmidt, 

 Koken, Bassler, and others, and some are field identifications. 



THE ORDOVICIAN SYSTEM. 



Introduction. The Ordovician was subdivided by Schmidt into the 

 following members which are named with their thicknesses (approxi- 

 mate only) from the summit downward. 



F2. Borkholm limestone. 20 ft. 



Fl. Lyckholm limestone. 50-60 ft. 



E. Wesenberg limestone. 30 ft. 



D3. Wassalem limestone. 10 ft. 



D2. Kegel limestone. 10 ft. 



Dl. Jewe limestone. 100 ft. 



C3. Itfer beds. 10 ft. 



C2. Kuckers shale. 10 ft. 



Cl. Echinosphaerites limestone. 30 ft. 



B3. Vaginaten limestone. 10 ft. 



B2. Glauconite limestone. 30 ft. 



Bl. Glauconite sandstone. 30 ft. 



Of these only the Lyckholm and Borkholm limestones come within 

 the writer's problem. 



Lyckholm formation. The most easterly known exposures of this 

 formation are along the lower course of the Pungern Brook just before 

 it empties into the northern end of Lake Peipus. Bending northward 

 the outcrops follow just north of the o9th parallel, and reach the sea 

 on the Nucko peninsula, north of the city of Hapsal. The Island of 

 Worms probably belongs wholly to the Lyckholm and there are exten- 

 sive outcrops on the northern side of Dago. The thickness of the 

 formation is not known exactly, but it is estimated to be about fifty 

 or sixty feet. 



