70 Transactions. 



to those reported on by Murray as occurring in the " Bottom deposits " 

 obtained by the " Blake."* 



The association of nodules with greensand does not, however, point to 

 a genetic connection between the two, since nodules are found on the bottom 

 of the present sea not associated therewith. They are of different origin 

 and character, as may be inferred from the report on the " Blake " deposits, 

 and as is noted in the report of the " Challenger." The point is well brought 

 out by Collet and Leef : — 



" La glauconie et ses concretions phosphatees se forment actuellement 

 sur le fond des mers, existe-t-il une relation entre ces deux formations au 

 point de vue de leur genese ? Cette question se pose naturellement quand 

 on etudie les depots marins, et nous croyons etre maintenant en mesure 

 d'y repondre negativement. 



" Les concretions phosphatees sont pour ainsi dire l'image du fond dans 

 lequel on les rencontre, ce qui prouve bien leur formation in situ. Ce fond 

 est-il sable vert, comme dans le cas de l'Agulhas Bank, les concretions 

 phosphatees contiendront de la glauconie en grand abondance ; est-il une 

 boue a globigerines formee non loin du continent mais en eau profondc 

 (3,475 metres pour un des echantillons du Challenger), la concretion sera 

 entierement formee de globigerines avec mineraux detritiques mais sans 

 glauconie." 



Therefore the association of the greensand with phosphate nodules in 

 the case of the limestones merely indicates that the nodules were formed on 

 a sea-bottom at such a depth that greensands were being laid down at the 

 same time. The depth was approximately that at which the limestones 

 also were being deposited, as is evidenced by the interstratification of 

 the greensand and limestone and the presence of glauconite grains in the 

 limestone. The Amuri limestone has been shown by Marshall (1916, p. 95) 

 to be practically equivalent to an ooze, and its chemical composition shows 

 that it contains over 80 per cent, of CaC0 3 , so that it may be concluded, 

 judging from the table given in the " Challenger " report (p. 79), that the 

 depth was under 1,000 fathoms. 



Microscopic Description of a Typical Nodule. — Under the microscope the 

 base consists of irresolvable matter, probably calcite, with numerous teste 

 of Foraminifera, and small fragments of quartz, feldspar, and occasionally 

 mica. The base contains patches of microspherulitic structure, exhibiting 

 between crossed nicols a well-marked cross with dark arms parallel to the 

 cross-wires. They resemble to some extent' small spherules of chalcedony, 

 but from their high polarization colours they are no doubt composed of 

 radiating fibres of calcite. There is a greenish stain of glauconite all 

 through the slide, and the mineral at times 'forms distinct grains, in many 

 cases filling the cavities of Foraminifera. These last are very numerous and 

 constitute the bulk of the rock. The following genera were recognized : 

 Globigerina (which is by far the most important), Textularia, Nodosaria, 

 Rotalia. Badiolaria are also present. The glauconite is light-green as a 

 rule, but occasionally dark-green and black aggregates also occur as a result 

 of the peroxidation of the iron present. Small fragments of bone were also 

 noted in one of the nodules. 



Nodular Limestone. — This second class of phosphatic material consists 

 of detached portions of the Amuri limestone included in the greensand. 



* Ball. Mus. Comp. Zool, vol. 12, p. 52, 1885-86. 



tRecherches sur la glauconie, Proc. Roy. Soc. Edin., vol. 26, ]>t. 4, p. 260, 1906. 



