PROF, T. M‘K. HUGHES ON SPONGIA PARADOXICA,. 277 
sections of joints with the bedding-planes or with one another. At 
the intersection of three or more such planes they spread out into 
triangular pieces or irregular flat masses according as these 
divisional planes have affected the infiltration and concretionary 
action. When the exterior part which should show the sponge- 
growth comes across an included fragment, it does not grow round 
it, as would a sponge, but shows a banded concretionary structure, 
as seen under similar circumstances in the ironstone concretions of 
the Lower Greensand or Oolitic series. 
The Red Rock itself is a concretionary bed; there is a pink gritty 
or conglomeratic limestone, with cavities filled with spar and slicken- 
sides, pervading it; where circumstances favoured the formation 
of concretions of uniform size and form, as was the case along the 
intersections of the joints and bedding-planes, there a symmetrical 
series was produced ; elsewhere the concretionary limestone occurs 
in large nodular masses in the more sandy matrix. So the occur- 
rence of flint in the overlying chalk is very much regulated by joints 
and bedding which facilitated, and clayey bands which impeded, in- 
filtration; but we have, in that case, the additional disturbing cause 
arising out of the fact that the silica was apt to be attracted by the 
traces of organic matter left in connexion with fossils. 
Phosphatic nodules are not uncommon in the lower part of the 
White Chalk; and it occurred to me that had these paradoxical bodies 
been sponges, they might have been phosphatized, as is so com- 
monly the case with the sponges of the Cambridge Greensand or 
basement-bed of the Chalk. 
Portions of the specimen exhibited have been analyzed in the 
chemical laboratory at Cambridge, through the kindness of Professor 
Liveing, who writes, “‘ My assistant has examined the specimen you 
sent to the laboratory; he does not find any very obvious difference 
in composition between the nodular part and the surrounding matrix. 
Both contain a small quantity of phosphate, but only a very small 
quantity, and it is as nearly as possible in equal proportion in nodule 
and matrix. 
*“‘ As to the green colour about the concretion, it appears to be due 
to silicate of iron; at the same time it may be due in some slight 
degree to some phosphate of iron ; for there is rather more phosphate 
in proportion to the whole mass in this green part than in the rest 
of the matrix ; but the whole quantity of phosphate is small in both.” 
In this respect it agrees with the nodules in the base of the Upper 
Chalk, near Swindon, some of which have been analyzed by Mr. 
Phillips, of St. John’s College, who informs me that there is nearly 
as much phosphate in the chalk which forms the matrix as there 
is in the nodules themselves. The only difference which can be 
detected is that which can be seen with the naked eye, namely, that 
the nodules and the so-called Spongia paradoxica often have a more 
hard stony character, due to incipient crystallization of the carbonate 
of lime.. 
It is always difficult to prove a negative; but it does seem to me 
that enough has been said to throw doubt upon the sponge-theory, 
