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. 
