406 



THE GEOLOGIST. 



specimens. For this reason, the author confined his observations m.ore especially 

 to the Spongilla fiaviatilis, specimens of which can readily be obtained of 

 small size, and presenting favourable conditions for the observation of their 

 porous system. As in the Hymeniaddon, the inhaled currents of water carried 

 rapidly in through the numerous pores, the floating particles of indigo, the 

 grosser pieces of which, with the flocculent and foscal 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 

 dliata, and not immediately around or within the pores." 



So little is known of the fossil sponges, and indeed, generally also 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 

 may not seem to have an immediate bearing, as it is only by the knowledge of 

 the recent forms that we can hope to make out and classify the extinct. 



The report of the Belfast Dredging Committee is an important document, and 

 interesting from the changes which have of late years taken place by t'le gradual 

 silting up of parts of the bay, and the consequent influences which these changes 

 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 more dense and specifically heavier, 

 until it reaches 40*^, after which, if we continue to elevate the temperature, 

 its density progressively decreases. Mr. Nasmyth finds that water is not a 

 singular and specinl 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, &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 w^as, 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 

 warrant him to allude further to its existence." 



The author considered these facts worthy of the attention of geologists as the 

 key to the explanation of many eruptive or upheaving phenomena, which the 

 earth s crust, and especially that of the moon, present — namely, that, on the 

 a]iproach 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, nnd also to express upwards, through the so- cracked surfaces, streams 



