Lacustrine and fluviatile deposits occur intermingled with the above.
In the great lacustrine depression of Nicaragua is collected all the drainage from the eastern versant of the volcanic mountains, from the sheer western escarpment of the main cordillera, and from a large area of northern Costa Rica.
The Lacustrine period has not yet reached its close in Russia.
The deposits of the Post-Glacial period are represented throughout Russia, Poland and Finland, as also throughout Siberia and Central Asia, by very thick lacustrine deposits, which show that, after the melting of the ice-sheet, the country was covered with immense lakes, connected by broad channels (the fjarden of the Swedes), which later on gave rise to the actual rivers.
But the great lakes which covered the country during the Lacustrine period have disappeared, leaving behind them immense marshes like those of the Pripet and in the N.E.