EXPLANATION OF THE PLATES. 
PLATE XVII. 
Fig. 1. Section from the northeast corner of Austerlitz to Stockport on the Hudson river, 
Columbia county. 
2. From the Massachusetts State line, to the city of Hudson. 
3. From Johnstown to Taghkanick, and thence to Copake lake, Columbia county. 
PLATE XVHI. 
Fig. 1. Section from Poughkeepsie to Sharon, Connecticut. 
2. From Poughkeepsie to Ameniaville. 
3. From Fishkill across the Highlands to the Connecticut State line, on the road to 
Danbury. 
PLATE XIX. 
Fig. 1. Fossil found in a boulder at Schoharie, by J. Gebhard junior. 
PLATE XX. 
Fig. 1. Fossil found at Schoharie, by J. Gebhard junior. 
PLATE XXL 
INFUSORIA. 
The sketches on this plate were all made by Prof. Bailey of West Point, by means of a ca¬ 
mera lucida eye-piece attached to Chevalier’s horizontal and vertical microscope. In fig. 39 is 
shown a sketch of xViths of a millimetre, magnified and drawn with the same combination of 
lenses, camera lucida, distance, &c. This being equally magnified with the drawings, will serve 
as a scale to determine the absolute dimensions of any of the objects. The highest power of 
the instrument was not used in getting the outlines, as it would have given figures inconven¬ 
iently large. The details were, however, occasionally corrected or confirmed, by the use of 
a higher power.* 
Fig. 1. Desmidium Schwartzii, from a twisted portion of a filament. 
2 and 3. Euastrum? two positions of same individual. 
4 and 5. Euastrum ? a larger variety of the same species as fig. 3. 
5. shows the same in side view, the lower half being in a state of imperfect develop¬ 
ment. 
Silliman’s Journal, Vol. 41. 
