1887.] Professor Sacco on Origin of Great Alpine Lakes. 283 
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P 
-M 
r 
' 
Terracian,* 
Retreat of the glaciers. Con- 
version of the great troughs 
into lakes. Powerful river 
erosion, accompanied by the 
formation of terraces. 
Alluvia, Peat. 
<y 
b 
Saharian— 
(2nd Glacial 
Epoch). 
Great development of glaciers : 
filling of the great troughs 
by ice. Enormous streams. 
Morainic amphi- 
theatres. Drift. 
Diluvium. 
General excessive elevation of the Alps and Apennines, and settlement of 
the existing Alpine orography. Formation or enlargement of many valleys, 
and of almost all the lake-basins by faults, folds, elevations, and subsi- 
dences. 
Astian — 
(1st Glacial 
Epoch. ) 
Commencement of the general 
elevation of the Alps and 
Apennines. Initiation of the 
great glacial development in 
the Alps. 
Continental fluviatile 
or lacustrine, or 
flu vio -glacial de- 
posits. Yellow 
and grey marine 
sands. 
Tertiary 
PlACENTIAN. 
General subsidence of the Alps 
and Apennines. 
Continental fluviatile 
deposits. Blue 
marine marls. 
Messinian. 
General powerful elevation of 
the Alps and Apennines. 
Outlining of the existing 
Alpine orography. 
Continental fluviatile 
deposits. Marshy 
deposits. 
2. On the Minute Oscillations of a Uniform Flexible 
Chain hung by one End ; and on the Functions 
arising in the course of the Inquiry. By E. Sang, LL.D. 
(Plate IX.) 
Twenty-seven years ago the writer submitted to the Royal 
Society of Edinburgh a paper on the minute oscillations of flexible 
pendulums, in which some new general laws were expounded. He 
proposes now to consider one case of the phenomenon more in 
detail. 
The investigation of extensive oscillations of a flexible system is 
far beyond the present powers of the calculus, and we are restricted 
to the consideration of disturbances not far from the mean position 
of the system. 
In the case of a thread having weights arranged on it at intervals, 
* The Terracian embraces the epoch that intervened between the Glacial 
and the Present, and corresponds to the Post-glacial of other geologists. 
