276 



THREE CRUISES OF THE " BLAKE. 



color. The surface was irregular, and presented many ovoid, smooth 

 projections, the lai'gest of which were about one centimetre in diameter. 

 The whole mass was overgrown with sponges, corals, and annelids. 

 (Fig. 189.) Imbedded in the concretion were two shark's teeth, re- 

 sembling Lamna, the larger being 2^ inches in length and one inch 



Fig. 189. — Concretion. 333 fathoms. (Blake Station .317.) |. 



across the base. This tooth is the same as many found by the ' Chal- 

 lenger ' in great numbers in the greater depths of the central Pacific, 

 frequently forming the centres of manganese nodules. In the speci- 

 mens from the deep water of the Pacific, the interior of the tooth had 

 been in every instance completely removed, only the hai'd outer dentine 

 remaining. In the tooth imbedded in this concretion, on the contrary, 

 the vaso-dentiue of the interior of the tooth is well preserved, in this re- 

 spect resembling the shark's teeth of the same kind found in various 

 tertiary deposits, as for instance in South Carolina and in the island of 

 Malta. The vessels of the tooth are infiltrated with peroxide of iron 

 and manganese, and phosphate of lime. The whole mass has a breccia- 

 like appearance, the several fragments being cemented by deposits of 

 carbonate of lime and manganese peroxide.^ 



^ " When thin sections are prepared 

 and examined \vith the microscope, the 

 preparation has a variegated appearance. 

 All the grains are closely cemented to- 

 gether. There are numerous sections of 

 pelagic and other calcareous foramini- 

 fera, of pteropods, and fragments of 

 echinoderms. The interior of the forami- 

 nif era is sometimes completely filled Avith 



calcite, and the same crystals are found 

 cementing many of the fragments of 

 which the rock is composed. Small frag- 

 ments of quartz, of feldspar, and of zoi- 

 ene are also seen in the sections. But the 

 most characteristic element is formed by 

 small rounded grains of a brownish or 

 yellow-green color, having much the as- 

 pect of glauconite, which is also present. 



