1887.] traidimj off Colombo in 675 Fathoms of Water. 211 



I made, in order to arrive at an approximate estimate of the propor- 

 tion of baric sulphate present, a determination of the sulphuric acid . 

 An average sample from two of the nodules powdered and dried at 

 100° C. gave 82*5 % ^^ baric sulphate, the whole SO 2 Ho ^ being calcula- 

 ted as SO^Bao". 



This result is, however, of course too high, as a small quantity of the 

 SOgHog is combined with Oa. and Sr. in the form of calcic and strontic 

 sulphates, though, from the results of the qualitative analysis, it is pro- 

 bably not much too high ; and we may, I think, safely take 75°/^ as the 

 percentage of baric sulphate present. 



In order to see whether the material was derived from the mud in 

 which the nodules occur, and which also contained Foraminifera, I made a 

 qualitative analysis of the mud, and found it to consist mainly of alumi- 

 nio silicate, with small quantities of calcic carbonate, some iron, and a 

 trace of manganese ; there was also a trace of an alkaline earth which 

 was not removed by boiling with hydrochloric acid and subsequent 

 washing, but this, on spectroscopic examination, shewed itself to be 

 lime. 



In spite of the negative result of the analysis of the mud, I am in- 

 clined to think, from the presence of the Foraminifera both in the mud and 

 enclosed in the nodules, that the latter have been formed at the bottom 

 of the sea either at the spot where they were found or at no great dis- 

 tance therefrom, though it is difficult to imagine how the material was 

 obtained, but it is possible that a careful analysis of a larger quantity of 

 the mud would reveal a trace of Barium, for sea- water contains a slight 

 trace of this element. 



I cannot at present call to mind any instance of sphaerulitic 

 structure occurring without the aid of heat. 



In volcanic lavas and in artificial glasses, it may be regarded as 

 concretionary, or as resulting from incipient crystallisation or devitri- 

 fication around certain points or nuclei. The nuclei when they exist 

 consist either of a granule or a minute crystal or crystallite, but most 

 commonly no nucleus is discernible.* 



In this case, however, it would seem, that it must be due to slow 

 segregative action; and, baric sulphate being very slightly soluble in 

 water, the deposition would be very slow and may have been to some 

 extent crystalline, at any rate sufficiently so to produce the same effect 

 as incipient crystallisation from a glassy mass. 



The execution of the accompanying plate has been kindly superin- 

 tended by Mr. J. Wood-Mason. 



* Uutley's Study of Eocks, p. 183. 



