SPONGKS. 

 Reduced analyses of formninijcra. 



SiOj 



(Al.Fe)s03 

 MgCOj.... 



CaCO, 



CajP-A... 



1 



0.03 



.19 



11.08 



88.70 

 .00 



100. 00 



0.31 



.13 



10.55 



89.01 



Trace. 



100. 00 



0. U 



.09 



10.04 



89.76 



Trace. 



I 0.02 



11.22 



88.76 



(?) 



0.56 



9.33 

 90.11 

 (?) 



100.00 ; 100.00 100.00 



In Xos. 1 and 2 the high percentages of silica and sesquioxides are e\ndenlly due to iiiipun- 

 ties If they are rejected, the percentages of magnesium carbonate become 5.19 and 2 09, 

 respectively. These two Foraminifera are from deep and presumably cold water. The othexs 

 are from shallow water in warm regions. A similar difference in the magnesian content of the 

 organisms with regard to temperature appears, with much regularity, in several other series 

 of ''our analyses, notably in the scries of crinoids and alcyonarians. ^ , , , 



The only published analyses of Foraminifera that we have been able to hnd elsewiicre 



appear in II. B. Brady's volume ' on the material collected by the Challenger expedition. Four 



of these analyses relate to Orbitolites complanaia var. ladmata, collected cither at Fiji or at 



' Tongatabu, Friendly Islands. These analyses are as follows: 



1, 2. Two different, sainplfs; analyses by C. R. A. Wright and J. T. Dunn. 



3! Sample washed with boiling water. 



4. Same as No. 3, unwashed; analyses 3 and 4 by J. Gibson. 



Analyses of orbitolites. 



SiO. 



A1,0. 



(Al,Fe)20: 



MgCOj 



CaCOa 



" Induding "phosphates of lime and magnesia.' 



Other analvses, presented by Wright and Dunn, are of AmvUstegina lessonn, from tape 

 Verde Islands, and Operculina complanata, from near Amboyna, in the Malay Archipelago Ihe 

 analyses are obscurely stated but give from 4.S to 4.9 per cent of magnesium carbonate, in 

 a Tertiarv fossil, Nuhecularia novorossica, 26 per cent of magnesium carbonate was toiind, an 

 amount which probably represents a concentration by leaching. There arc also analyses of 

 several sihceous Foraminifera containing from 76. 1 to 94.7 per cent of silica. 1 heir tests appeal 

 to have been built up of sand grains and are of little or no sigmficance in relation to the main 

 problem of the present investigation. Their remains are not true additions to the sediments. 



SPONGES. 



The sponges are a rather unsatisfactory group of organisms for chemical analysis, on account 

 of their very porous structure. Thev are liable to contain inclosed impurities, such as sand 

 or mud, which are difficult to remove entirely. Some sponges are siliceous, some calcareous 

 and others are composed almost wholly of organic matter, the proteid spongin. Ihc ideal 

 method of procedure for our purposes would obviously be to separate the clean sihceous or cal- 

 careous spicHiles an.l to analvze them alone, but to do that a large amount of material would have 

 to be gone over, and more time would be consumed than we could give to this part of our investi- 



I Brady, H. B., Chalknger Kept., vol. 9, pp. .wii-xxl, 1884. 



