210 E. J. Jones — On some Nodular Stones obtained hy [No. 2, 



On breaking them open, the fractured surface has much the appear- 

 ance of an ordinary slate without the cleavage, and is of a much darker 

 colour than the exterior. Running along the central line of a long 

 cylindrical one which I broke open, there is a narrow vein of a brownish 

 colour. 



A microscopic examination of a thin slice shewed merely a confused 

 mass of aggregates resembling in their structure that of sphserulites, 

 such as occur in the so-called sphaerulitic lavas, with the remains of 

 Foraminifera and Radiolaria disseminated throughout the mass. With 

 ordinary light, little is to be seen except more or less radiating fibrous 

 aggregates, but, as soon as the section is observed between crossed 

 Nicol's prisms, the whole field is seen to be covered with little dark 

 crosses with their limbs parallel to the planes of the prisms, and, on 

 revolving the stage, the limbs of the crosses keep the same orienta- 

 tion whilst the section revolves. 



It is when thus observed that the aggregates are seen to be entirely 

 distinct from one another, as each cross keeps to its own aggregate, 

 and the crosses do not overlap ; so that, by revolving the stage, the limit 

 of each aggregate can be determined by tracing the path of the outer end 

 of one of the limbs of the crosses. 



In the volcanic rocks in which this structure is known, it appears 

 to be due to incipient crystallization in a glassy mass ; and at first it 

 might be supposed that these masses were of igneous origin. This idea, 

 however, is untenable on account of the remains of Foraminifera 

 (of several species, the most easily recognised of which are the 

 globigerinae) and Radiolaria which are sparsely scattered through the 

 mass and, in some cases, enclose a sphsDrulitic aggregate. 



An indeterminate greenish substance, which probably consists of 

 glauconite, is also seen scattered through the mass. 



The only difference that can be detected between the central vein 

 and the portion between it and the exterior is that the aggregates in 

 the central vein are much larger and the colour brown instead of 

 green, and that it is unacted on by hydrochloric acid, which dissolves 

 out some calcic carbonate from the other portion. 



As mentioned by Mr. Daly in his letter forwarding the nodules, 

 these are very heavy, having a sp. gr. of 3* 77 at a temperature of 30° 0. 

 as against water of 4° C. 



A qualitative analysis shewed the nodules to consist in great part 

 of baric sulphate together with small quantities of calcic and strontic 

 sulphates, small quantities of calcic and magnesic phosphates, aluminic 

 silicate, calcic carbonate, and traces of iron, sodium, and manganese. 



Not having the time to devote to a complete quantitative analysis, 



