288 The American Geologist. November, looi. 
weak and but little above the level of sedimentation, the silts 
are seen to have encroached from all sides and to have filled 
the depressions in the irregular surface [PI. xxvii, Fig. 2], 
some times nearly or quite covering the mass. Usually these 
encroachments are one-sided, depending upon the configuration 
of the mass and possibly upon the direction from which the 
currents came. In such cases the surviving life, starting up 
afresh, is seen to have formed a new growth often quite dis- 
tinctly defined and resting well over upon one flank of the 
parent mass. In many cases this was repeated several times, 
though not always so conspicuosly, the surviving life each time 
lying in a little different quarter. The limestone layers extend- 
ing in upon these thin shale partings to the new life centers, 
are often flexed and thinned before being augmented by the 
local growth. [PI. xxvii, Fig. 2.] Silt patches usually pro- 
duce an imperfect layering within the lenses and sometimes 
recurring several times in the same vertical line, produce a 
bedding corresponding roughly with the planes of sedimenta- 
tion without. Figure i, plate xxvii, is of a mass which ap- 
pears to be made up of two nearly independent growths of 
fistuliporids, with slightly diverging axes. The imperfect lay- 
ering in the space between the two halves, was maintained by 
silt pocketing. 
In some instances life may have been completely smothered 
out and the elevation remaining became later the site for new 
fistuliporid colonies. This is difficult to determine, owing to 
some part of the mass always being broken away or remaining 
imbedded. Of two neighboring masses, on the Genesee, the 
growth of one is seen to have stopped at a certain silt plane, 
while the other is divided by it into distinct upper and lower 
portions. It is the impression however that there must have 
been some life connection between the two growths. 
Another mass at the same locality had somewhat the shape 
of an hour-glass. The narrow neck of lens rock which connect- 
ed these two parts or lenses, probably represented the thread of 
life surviving the silt girdling. This life at last regaining vigor 
and extent was finally smothered out by another and heavier 
blanket of fine mud, indicated by the shale w^hich covers its 
summit. 
