a 
TWENHOFEL: EXPEDITION TO THE BALTIC PROVINCES. 329 
between fifty and seventy-five feet are represented, consisting of a 
complex of dolomites, limestones, and shales. In the interior of Ogesel 
to the northwest of Arensburg, the rocks are chiefly yellow erystalline 
limestones, and dolomites and a similar lithology obtains on the 
northern end of its outcrops on the western shores, to as far south as 
Sarepa. 
On the south coast to the east of Arensburg, the strata consist of 
heavy-bedded limestones and shales, and the lithic facies on the 
Sworbe to the southwest of the city is very like that of the southern 
coast, although there is not so much of the massive limestone, and 
calcareous shales appear to haye a larger representation. These 
strata are younger than those described in the preceding paragraph. 
Since there are two lithic units in this division it may ultimately 
prove necessary to give formational rank to each. I have hesitated 
to do this because of the apparent impossibility of determining a basis, 
or locating a plane of division. The latter, however, is a common and 
almost universal difficulty throughout the Esthonian region. None 
has been determined between the St. Johannis and this formation, 
but the latter is assumed to begin with the appearance of Whitfieldella 
didyma (Dalman), W. prunum (Hisinger) and the eurypterids. For 
convenience, however, the two divisions of this formation will be 
described as the Sagaristi and Kaugatoma zones, after the localities 
which are considered typical of the lower and upper divisions. 
(a) Sagaristi zone. The most northern and lowest exposures of 
the interior are those of Sagaristi, Uddafer, and Ladjal. At Sagaristi 
not more than four feet of strata are exposed, consisting of interstrati- 
fications of coarsely crystalline gray and yellow limestones (beds one 
to three inches thick), white to yellowish white poorly or finely 
crystalline dolomitic limestones and thin calcareous shales. The 
dolomitic limestones appear to be much used for flags and building 
stones. Fossils are extremely common in patches, but the fauna is 
dominated by the abundance of Whitfieldella didyma and Rhipi- 
domella hybrida. The former in some places occurs by hundreds. 
The same strata with a similar lithology are well exposed in quarries 
extending from Uddafer to Ladjal, but the thickness shown is con- 
siderably greater. The following fossils have been collected from 
these localities: — . 
1. Clathrodictyon vesiculosum. 
2. Favosites gothlandicus. 
3. Laceripora cribrosa Eichwald. 
