RAYMOND: CORRELATION OF THE ORDOVICIAN STRATA. 183 



occur are composed of glacial debris. Along the whole northern 

 boundary of the area there is an abrupt escarpment, facing northward, 

 extending from the island of Odensholm through Baltishport and 

 along the southern shore of the Gulf of Finland to the mouth of the 

 Narowa, and thence across country south of Petrograd to the Sjass. 

 Where this borders the sea it is usually very steep, often perpendicular 

 or overhanging. In the Government of Petrograd it is a steep slope, 

 but usually without exposures of rock except where cut by streams or 

 by the opening of quarries. This cliff, or " Glint," ^ is of variable 

 height; only fifteen feet on Odensholm, it reaches its maximum height 

 of 206 feet at Ontika in the eastern part of Esthonia, and probably 

 averages 75 to 100 feet. The strata composing the top of this cliff 

 are, remarkably enough, practically always the same, being the rather 

 hard magnesian limestone of the lower part of zone C or the " Echi- 

 nosphaerites" layers. Such being the case there are many excellent 

 exposures of the part of the Ordovician below this horizon, and, 

 where there is not too much talus at the foot of the cliff, the upper 

 part of the Lower Cambrian is usually shown. 



From Petrograd eastward, no strata of the Ordovician are exposed 

 above the Echinosphaerites beds. The higher strata are to be found 

 in the part of the Government of Petrograd west of the metropolis, 

 and especially in the Government of Esthonia. These beds are very 

 seldom seen in natural sections, being practically always uncovered 

 only by the opening of quarries. All the quarries are of comparatively 

 small extent and very shallow, so that there is never more than one 

 formation exposed in any one quarry, and contacts between forma- 

 tions above the Kuckers have never been seen. 



Over large areas in Esthonia the strata lie very close to the surface, 

 and even very shallow ditches often penetrate the rock. Among such 

 ditches the "Graben" on the estate of Baron Toll at Kuckers, near 

 Jewe, is famous as the principal locality of the Kuckers formation. 

 Many other ditches, often very small ones, were examined during this 

 trip and often afforded the only outcrops over considerable areas. 



FORMATIONAL NaMES. 



The names applied to the formations in this district of Russia bear 

 a direct relation to the above described occurrence of outcrops. In 

 the classification proposed by Schmidt the important divisions of the 



1 From the Danish Klint, a reminder of the settlement of this country by the Danes in 

 the 12th century. 



