the Greensand compared with those of existing Species. 135 



make use of such elements for building up their habitations. 

 But be this as it may, the axial canals of the deciduous 

 spicules, both entire and fragmentary, in the spiculo-arenaceous 

 sponges and the head of S<iuamulina scojjula are for the 

 most part unusually large. 



Concluding Remarks. 



In accounting for the Haldon deposit geologically, with 

 reference to the fossil spicules of the Spongiada? which it con- 

 tains, we have to consider whence the sand of Avhich it is 

 composed w^as derived, to what kinds of the Spongiadas the 

 fossil spicules in it belonged, in what kind of climate these 

 sponges probably lived, what kinds of the Spongiadaj are not 

 represented in the deposit, and, lastly, by what agency its 

 elements were brought together. 



These queries can be soon answered. 



In the first place, the sand, coming from the disintegration 

 of older rocks, was probably of shore origin. Then, the kinds 

 of Spongiadaj to which the fossil spicules contained in it be- 

 longed (at least those which can be recognized) are the Pachy- 

 tragias and the Coralliospongia3, including the Euplectellidte, 

 the former of which now grow in the marginal zone of the 

 sea, and the latter in the zone immediately following it, — that 

 is to say, the Euplectellidaj at the Philippine Islands in 10 to 

 24 fathoms (Cuming, ajnid Bowerbank, /. c.) and the Corallio- 

 spongiai in 98 {SympageUa mix, Sdt.) to 700 {AphroccdUstes 

 Bocagei, Wright) : none of those referred by M. de Pourtales 

 to Dr. Schmidt were found below 450 ; and Aphrocallistes 

 Bocagei was also found by Dr. W. Thomson in 700 fathoms. 

 The Pachytragia3 appear to be world-wide in habitat, and the 

 Coralliospongiai confined to the warmer latitudes and the 

 equatorial region of the sea. No spicules of the Calyci- 

 spongife (Kent) or deep-sea sponges, such as Ilyalonema, Hol- 

 ^eM<'6r,&c.,have been found in this deposit, the materials of which 

 must have been brought together by strong tidal currents. 



It follows, then, that, the sand being of shore origin, the 

 Pachytragiai and CoralliospongiEe living in the marginal and 

 following zones of the sea respectively in warm latitudes, 

 while tidal cmnrents requisite to drift into one and the same 

 deposit such coarse materials are also chiefly confined to these 

 regions, the deposit was formed rather nearer the shore than 

 the deep sea, and in a climate much warmer than our pi-esent 

 one. 



Again, the sandy nature of the deposit, and the absence of 

 all fossil spicules like those of the deep-sea sponges, contrast 



