292 bulletin: museum of comparative zoology. 



who takes exception to some of Bassler's conclusions relating to the 

 stratigraphy. A work which discusses the history, archaeology, 

 stratigraphy, and natural history of the Russian Baltic provinces 

 appeared in Riga in 1911, and bore the title, Baltische Landeskunde. 

 It was the work of several writers, that which pertained to the Palaeo- 

 zoic geology having been written by A. von Mickwitz. It is a good 

 work for general reference. 



Introductory discussion of the Esthonian section. The entire se- 

 quence of the Russian Baltic section consists of evenly bedded, almost 

 horizontal limestones and subordinate shales with an occasional thin 

 division of sandy material. There is a very gentle dip southwest- 

 ward, generally imperceptible. The entire Ordovician and Silurian 

 may have a thickness of 725 feet, of which about 350 feet are 

 Ordovician and 375 feet Silurian. 



Natural outcrops are not common, rarely existing save at the 

 seashore, where the Cambrian and basal divisions of the Ordovician 

 are exposed in the cliffs, or, as they are called in Esthonia, glints. On 

 the island of Oesel the Silurian is exposed in the sea cliffs, which on 

 this island are known as panks. Had one to depend on natural 

 exposures little could be learned of the stratigraphy of the land a few 

 miles distant from the sea. Everything is grassed over and, if a 

 surface be made bare, a few years suffice to completely cover it again. 

 Fortunately, however, the need of limestone for burning or con- 

 struction purposes in the past, led to the opening of many small 

 quarries, and in later times artificial exposures have been further 

 increased by the digging of ditches for the drainage of swamps or 

 roads. Through these, a partial understanding of the stratigraphy 

 of the interior has been attained. Of late years the demand for lime 

 and stone appears to have decreased, or to have been supplied from 

 elsewhere, since many of the quarries studied by Schmidt are now 

 wholly or partially grassed over, so that their examination is difficult, 

 and, in some cases, impossible. Large cement plants have been built 

 at Port Kunda and Asserian, and these have developed extensive 

 exposures of the lower divisions of the Ordovician ; but nothing of the 

 higher beds. 



Up to the present it has been impossible to learn the exact sequence 

 of strata above the Echinosphaerites limestone and it is rare that one 

 is able to discover the contact of any formation with those adjacent. 

 Hence the determination whether certain strata are continuous with 

 others, from which they differ through horizontal variation of sedi- 

 ments, or whether they lie at a different horizon, has not been possible. 

 It will probably be long before the sequence is completely known. 



