Clinton and Niagara Strata. — Sarlc. 291 
rock splinters reveal a structureless bluish gray surface, with 
no trace of organic contents. 
The lenses at Niagara and vicinity generally exhibit a more 
uniform aspect than those in the eastern portion of the area, 
due to the smaller percentages of silts, the upper ten feet at that 
locality forming a solid bench. [PI. xxviii. Fig. 4.] 
Owing to the well defined bedding planes in the limestone 
at Rochester, [PI. xxvii. Figs, i and 2.] these features may 
all be studied there to particular advantage, affording an un- 
equaled opportunity for comparisons. It is possible to trace 
any of the shale partings from one neighboring mass to an- 
other, thus enabling one to see its relation to several of these 
growths, or to examine several limestone floors in their vicinity 
in the same way. 
While these masses were similarly afifected by general con- 
ditions yet in each we find many features that are specific ; 
showing that each lens had a history differing from that of 
every other. 
ASSOCIATED LIFE. 
Attached Forms: — The associated life usually found upon 
these fistuliporid masses shows them to have been mainly cen- 
ters for other attached forms. This is probably due to the fact 
that the free larva of the smaller and more delicate bryozoans, 
and of brachiopods in particular, required some firm base for 
attachment. Freely distributed in the sea, they settled every- 
where, but lived in greater numbers upon these hard surfaces, 
there finding this prime essential to their existence. One of 
the best examples of this is found in Niagara gorge on the 
New York Central and Lewiston railroad, at the third watch- 
man's hut. [PI. xxix, Fig. 6.]. This mass is thirty feet 
long and ten feet high. Brachiopcds probably make as 
high as thirty per cent, of the contents. In some 
Darts their shells are so abundant as apparently to 
have nearly smothered out the bryozoan nucleus. In 
the mass proper the brachiopods are entire and appear to have 
been largely covered by the bryozoan growth, thus preserving 
the valves intact. Some of these are evidently in position of 
growth. 
Other Forms: — Thus inhabited these sites attracted other 
forms which in turn drew others, until they became rich feed- 
