38 BlCTYOSPONGID^ 



the nature of their habitat ; for in many instances there is collateral evidence 

 of the sponge having been drifted from its proper position. 



The known colonies of these sponges afford more direct evidence. The 

 colony of Hydnoceras Bailiense, at Bath, lies overwhelmed between banks of 

 sandstone and involved in a few inches of a somewhat arenaceous clay-shale. 

 Its existence was terminated abruptly, as shown by the fact that the great 

 majority of the individuals are confined to a very thin layer at the surface, of 

 the sandstone and by the additional fact that all have been greatly compressed. 

 Now it is found that while the exposed surface of these overw^helmed sponges 

 may be covered with the slialy rock, their under surfaces are involved in the 

 sand and, further, occasional specimens are found quite buried in the sandstone 

 stratum itself. It is possible that this extensive sponge plantation grew upon 

 the muddy bottom represented by the thin layer of shale, though the data 

 more clearly indicate that it was rooted on the sandy bottom and was over- 

 \vhelmed by the influx of mud. A great number of specimens of Hydtioceras 

 hotroedenm have been taken from the soil on Irish hill, near Bath, and though 

 the rock beds from which they come have not }^et been opened, the specimens are 

 uncompressed internal casts in sandstone, both their form and matrix indicating 

 the absence of a muddy sediment. Tie colony of Hydnoceras kibei'osum at 

 Brown hill, near Cohocton, that on Hamlin's farm, near Naples, and the one at 

 Cotton hill, near Avoca, in the last of Avhich is a number of diverse species, are 

 all in a soft sandy sediment, which is highly laminated and schistose but is not 

 shaly nor does it show other evidence of muddy bottom except so far as the mud 

 is commingled with the sand. At Cuba, Allegany county, is a small colony of 

 Dictyospongia meptrwin which occurs in a heavy sandstone stratum and the 

 sponges have been prostrated not by any change in the nature of the deposit, 

 but rather by the impact of the waves or water currents. This is indicated 

 in the accompanying cut which shows three overthrown individuals lying 

 side by side and parallel, having evidently fallen where they grew. 



In other cases there is evidence of considerable admixture of muddy 

 matter in the sediment, as in the colony of Thysanodictya Edwin-Halli at 

 Wellsville, where the rock is soft and the specimens in large part compressed ; 

 but even here the matrix is still arenaceous and many specimens are without 

 compression. In this plantation from which several hiindred specimens have 

 been taken, the sponges are found at times to retain their upright position, 

 thus indicating how gently the sediments have been deposited about them. 

 Fifty miles away from Wellsville, which may be regaj-ded as the geographic 

 center of the most prolific sponge region in the upper Chemung beds, occurs 



