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. | 
D1. Jewe limestone. 100 ft. 
C3. Itfer beds. 10 ft. 
C2. Kuckers shale. 10 ft. 
C1. 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 59th parallel, and reach the sea 
on the Nuck6 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. 
