276 PROF. T. M‘K. HUGHES ON SPONGIA PARADOXICA. 
the view that it was the root portion of a sponge allied to Si- 
phonia; for the masses are of approximately uniform thickness, 
and terminate in rounded ends in the same plane as the rest of the 
fossil, or taper off along joints into banded rock, such as is due to 
infiltration; and in no case can I learn that any head has been 
seen attached to, or been found in connexion with, these branching 
anastomosing rootlike masses. It extends in a network uninter- 
ruptedly over many yards of rock, apparently, indeed, over the 
whole bed. The meshes are from 1 to 5inches across, more or less. 
It cannot be regarded as representing bounding portions of sareode 
round canals, as there is no depth to the structure; it is merely a 
very open net of a material rarely thicker than a one-inch rope ; 
nor can it be referred to a trailing anastomosing ramose sponge, as 
it occurs in vertical as well as in horizontal planes; and these 
vertical or highly inclined planes along which it occurs appear 
commonly to coincide with the joints. 
Another body to which the name Spongia paradoxica has been 
sometimes given is common in the same beds. It consists of 
masses of more crystalline texture, which exhibit upon the weathered 
surface a fretted network of small ridges enclosing cuplike depres- 
sions of irregular form and size, such as are not uncommonly seen in 
certain beds belonging to the Mountain-Limestone, or more exactly 
like some weathered surfaces of gypsum, where they obviously 
depend not only on the unequal texture of parts of the limestone 
or gypsum, but also upon the accidents that determine the limita- 
tion of drops upon a window, of the dotted moss and lichens that 
guide the formation of the weathered holes in limestone which are 
often mistaken for pholas-burrows, or of the cavities in the fretted 
surface of ice or rock-salt. 
These fretted surfaces are seldom found upon the trailing ramose 
bodies above described, which have a smooth exterior and are of 
approximately uniform thickness, whereas the fretted masses are 
tuberous lumps of all sizes up to 4 or 5 inches in diameter; but 
there is no reason for considering that the fretted masses are organic 
any more than the others. They show no internal structure, and 
the peculiarity of form and of surface has been shown to be just 
like that found in other weathered concretionary bodies. 
A microscopic examination of sections cut across these bodies often 
shows a more compact crystalline structure than that which is seen 
in the other part of the rock; but in other respects it is the same, 
and contains the same fragments of shell, &c., and the same grains 
and pebbles. 
Seeing, then, that there are so many and great difficulties in the 
way of accepting the view that these bodies represent the outlines 
of sponges, we must next ask whether there is any other probable 
explanation of them; and an examination of them in place suggests 
the idea that they may be merely concretions, owing their symmetry 
of form and regularity of arrangement to rock-structure, which is 
more obvious in the cliff than in hand-specimens. 
First, we notice that in a general way they run along the inter- 
