406 
THK GEOLOGTST. 
sijtcimens. For this reason, the author confined his observations more especially 
to the SpongiUa jliioiaiHia, specimens of which can readily be obtained of 
small size, and presenting favourable conditions for the observation of their 
porous system. As in the Ilymeniacidon, the inhaled currents of water carried 
rapidly in through the numerous pores, the floating pai tides of indigo, the 
grosser pieces of which, with the flocculent and foccal matter, were ejected through 
the osculum. The period of violent action corresponding, as in the marine 
species, to the time of feeding, and resolving itself sometimes suddenly and some- 
times gradually into the languid, or digesting and aerating, condition. When the 
incurrent action became rather languid. Mr. Bowerbank tells us he observed 
" That the molecules within the sponge were performing a sort of cyclose circula- 
tion, frequently rising up and passing across the open pores, but never coming 
out through them ; but every now and then a molecule of indigo would pass 
languidly into the pore. It would seem, therefore, to indicate that the organs of 
incurrent action were situated within the intermarginal cavities, as in Granta 
ciliata, and not immediately around or within the pores." 
So little is known of the fossil sponges, and indeed, generally ahso of the living 
species, that whatever tends to elucidate the structure and habits of this obscure 
class, cannot but be of value in the study of the extinct forms, even though it 
niny not seem to have an imnlediate bearing, as it is only by the knowledge of 
the recent forms that we can hope to make out and classify tlie extinct. 
The report of the Belfast Dredging Committee in an important doci'.ment, and 
interesting from the changes which have of late years taken place by tiie gradual 
silting up of parts of the bay, and the consequent influences which th( -e clianges 
have had upon the organic life of the region, especially upon the various species of 
mollusca. 
In the section of Mathematics and Physics is an interesting paper by Mr. J. 
Nasmyth, " On some Phenomena connected with Molten Substances." The great 
fact to which he drew attention was, "that all substances in a molten condition 
were specifically heavier than the same substances in an unmolten state." Hitherto 
water has been thought to be a singular and special exception to the ordinary law, 
that as substances were elevated in temperature they became specifically lighter, 
that is to say, that water at the temperature of 32", on being heated, does, on its 
progress towards temperature 40", become uiore dense and specifically heavier, 
until it reaches 40", alter which, if we continue to elevate the temperature, 
its density progressively decreases. Mr. Nasmyth finds that water is not a 
singular and special exception in this respect, but that, on the contrary, this 
phenomenon, in relation to change of density, when near the point of solidifica- 
tion, is shared with every substance with which we are familiar in a molten state. 
It is on account of this general law that, if we throw a piece of solid lead into a 
pot of melted lead, the solid or unmolten lead will float in the fluid or molten 
metal. The same holds good with respect to lead, silver, copper, iron, zinc, 
antimony, bismuth, glass, pitch, resin, wax, tallow, A'c. The normal condition as 
to density is resumed, in most substances, a little on the molten side of solidifica- 
tion, and in a few cases the resumption of the normal condition occurs during the 
act of solidification. 
Mr. Nasmyth also stated, " that from experiments which he had made, he had 
reason to believe that by heating molten metals up to a temperature far beyond 
their melting-point, the point of maximum was, as in the case of water at 40", 
about to be passed ; and that at such very elevated temperature the normal state 
as regards reduction of density by increase of temperature was also resumed; but 
that as yet he has not been able to test this point with such certainty as to 
waiTant him to allude further to its existence." 
The author considered these facts worthy of the attention of geologists as the 
key to tht; explanation of many eruptive or upheaving phenomena, which the 
earth's crust, and especially that of the moon, present — namely, that, on the 
approach to the point of solidification, molten mineral substances beneath the 
solid crust of the earth must expand, and tend to elevate or burst up the solid 
crust, nud also to express upwards, through the so- cracked surfaces, streams 
