730. 
Lastly, new data are offered: in respect to the southernmost 
limit of the northern blocks described on a previous occasion (ante, 
p. 405), and their further advance to the south in some situations 
than in others, is attributed. to the form of the present continent of 
Russia in Europe, nearly all of which, it is presumed, was under the 
sea during the distribution of these boulders. 
The authors adhere to the opinion previously expressed by them, 
that such blocks were transported.to their present positions by huge © 
floating icebergs, arrested, in some instances, by rising grounds and 
hills at the bottom of the then sea, and in others permitted to ad- 
vance further south by longitudinal depressions, which are traceable 
in the present configuration of the land. Proofs are given that in 
many instances blocks of trap and quartz rock advance to. quite as 
southerly latitudes as those of granite, and that all these blocks can 
be traced back to their, parent rocks in Russian Lapland and the 
northern parts of Russia in a north-nortl-westerly direction, the 
currents by which they were transported having therefore been di- 
rected to the south-south-east. The black earth or Tchornoi Zem, 
which forms the highest deposit of the central and southern regions 
of the empire, has been described in a previous memoir (See anée, 
p. 12). 
A large geological map of Russia in Europe, coloured by the 
authors, and numerous sections and collections of fossils, illustrated 
this communication, and it was announced that other conclusions 
respecting the structure of Russia would follow the description of 
the Ural Mountains. 
