36 MULLION ISLAND. 



In Messrs. Murray and Eenard's Report on the Scientific 

 Results of the Voyage of H.M.S. Ghalienger*' we find the 

 following entry during their voyage from the Admiralty Islands 

 to Japan. 



" Siliceous shells and skeletons were especiallj abundant in 

 some of the deposits in this section, more numerous than in any 

 deposits previously met with during the cruise. In one instance 

 these beautiful little organisms made up about fths of the deposit, 

 which was in consequence called Radiolarian Ooze. This was 

 the case in the deepest sounding, viz: 4,475 fathoms (over 5 

 miles), the greatest depth from which a specimen of the bottom 

 had hitherto been obtained." 



A map is annexed by these gentlemen, giving approximately 

 the nature of the ocean floor over the whole globe. They 

 estimate that 2,290,000 square miles of the ocean floor is covered 

 by Radiolarian ooze at a mean depth of 2,894 fathoms. They 

 find that this ooze contains only 4*01 per cent, of calcic carbonate, 

 and they consider that Diatoms and Radiolaria play a much more 

 important part in separating the soluble silica from the sea water 

 than do the siliceous sponges. This Radiolarian ooze of the 

 deep Pacific will consolidate in the course of ages into the 

 Radiolarian chert of the present era. 



The specimen of rock from the Mullion Island in your 

 Museum shows the Radiolarian chert traversed by a network of 

 white quartz veins with alternate layers or bands of chert and 

 shale. Thirty distinct bands of chert may occur in a thickness 

 of 3 feet of rock. These bands show signs of having been 

 compressed when plastic, and have also been faulted since they 

 solidified. Radiolarian ooze can only be deposited in seas 

 where there is little or no mud. Each band of chert is mainly 

 composed of the exquisitely reticulated skeletons or tests of 

 Radiolaria. A vast period of time may have elapsed during the 

 deposition of radiolarian skeletons suflScient to form a single 

 band of this chert. The alternation of chert and shale bands 

 may be accounted for by the supposition that a submarine volcano 

 introduced so much mud into the ocean as to prevent the silex 

 of the Radiolarian skeletons from binding, and thus for a period 



*Peep Sea Deposits, 1891, p. 175. 



