twenhofel: expeditiox 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 Oesel 

 to the northwest of Arensburg, the rocks are chiefly yellow crystalline 

 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 have a larger representation. These 

 strata are 3'ounger than those described in the preceding paragraph. 



Since there are two lithic units in this di^•ision 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 WhitfieldeUa 

 didyma (Dalman), IF. priinum (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 WhitfieldeUa 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. 



