Reports and Proceedings—Geological Society of London. 231 
freshwater lakes, nor is there any possibility that the shells can have 
been wasbed into the sea by rivers and then re-deposited in the 
beaches. The author believes that these-beaches were formed at a 
time when the Baltic was a freshwater sea containing a molluscan 
fauna whose principal representatives are the above-named species 
of Ancylus and Limnea. 
There are also on the Isle of Gotland raised beaches of marine 
origin containing Litorina, ete., which are seldom at a higher level 
than 50 feet, though one has been described by Lindstrém near 
Wisby, which is 80 feet above the sea-level. The marine raised 
beaches are, however, at a distinctly lower level than those with 
freshwater shells, and must have belonged to a later period, when 
the freshwater fauna had been supplanted by marine forms. 
Shell-beaches of a similar character and relative position, and con- 
taining the same freshwater mollusca, have been described by Friedr. 
Schmidt in Esthonia and on the islands of Osel and Mohn, but this 
author regards them, in part at least, as river-deposits, although there 
are no distinct traces of old river-beds in the localities where they 
occur.! Prof. James Geikie has also referred to these Russian 
deposits as indicating that the Gulfs of Finland and Bothnia were 
freshwater seas at the close of the Glacial period. 
Further discoveries are requisite before it is possible to lay down 
approximately the limits of the Baltic at the time when these 
Gotland freshwater beaches were formed, or to ascertain the nature 
and position of the barrier which dammed its waters 150 feet above 
their present level; but the author concludes that its northern half 
at least, together with the Gulfs of Finland and Riga, formed at the 
time a single freshwater basin. Ge dig Jal 
III SOuseitsS YNaNmDy 1-25, Cz aso IAN Ke TS - 
———__ 
GEOLOGICAL Society oF Lonpon. 
I.—March 28, 1888.—W. T. Blanford, LL.D., F.R.S., President, 
in the Chair.—The following communications were read :— 
1. “On some Eroded Agate Pebbles from the Soudan.” By Prof. 
V. Ball, M.A., F.R.S., F.G.S. 
The majority of the pebbles in a collection made by Surgeon- 
Major Greene in the Sondan, and presented by him to the Science 
and Art Museum in Dublin, are of very similar character to the 
agate and jasper pebbles derived from the basalts of India. It may 
be concluded inferentially that they came originally from a region 
in which basaltic rocks occur to a considerable extent. A certain 
number of them are eroded in a manner unlike anything noticed 
in India, though it is probable that similar eroded pebbles will 
eventually be found there. 
Throughout India, wherever there is deficient subsoil-drainage 
or excessive evaporation and limited rainfall, salts are apparent 
either in supersaturated subsoil-solutions or as crystallizations in 
1 Prehistoric Europe, p. 470. 
