264 Mr. J. D. Macdonald on Deep Soundings in the Pacific, 



XXV. — Further Observations on Deep Soundings obtained by 

 H.M.S. " Herald," Capt. Denham, R.N., F.R.S., employed on 

 Surveying Service in the South-western Pacific ; with an Ac- 

 count of the Examination of the Alimentary Matter of the 

 Salpae as bearing on the nature of the Materials composing the 

 Sea-bottom. By John Denis Macdonald, Assistant- Sur- 

 geon. 



[With a Plate.] 



The following observations are intended as an appendix to a 

 former paper, on the microscopic examination of the bottom 

 obtained in two soundings taken in the Eeejee group, from the 

 respective depths of 1020 fathoms and 440 fathoms. To these 

 positive soundings we can now add several others of much in- 

 terest, the most important of which, however, was registered on 

 the 30th May 1856, when, in latitude 30° 25' S. and longitude 

 161° 57' E., and about forty miles E. by S. of the reported 

 position of the Lady Nelson Shoal, a deep cast was taken, bring- 

 ing up bottom from a depth of 919 fathoms. 



Unfortunately, the greater part of the materials had been 

 wasbed away during the ascent of the lead through the water ; 

 and it was only with the help of the microscope that many 

 Foraminifera, siliceous spicula of Sponges, and the fragments 

 of the solid parts of more minute organisms were detected. 

 Enough, however, was retained in contact with the arming of 

 the lead, to prove that the bottom had been reached. Indeed, 

 this microscopic test is often in requisition, for in several in- 

 stances we have been enabled by its aid to pronounce with cer- 

 tainty, where the most scrupulous examination by unaided vision 

 had failed to decide. 



It may be mentioned here, that when the deep sounding in 

 1020 fathoms, above alluded to, was obtained, a double lead was 

 employed, and the greater part of the matter which had been 

 submitted to microscopic analysis was taken out from between 

 the strands of the lashing, very little being at all visible on 

 the arming. While these facts show how readily one may be 

 deceived in a matter apparently so easily determined, they sug- 

 gest the adoption of some simple apparatus, by means of which 

 a reasonable quantity of those minute materials might be safely 

 brought up from the bottom, both for inspection and preservation. 



As legitimately connected with this subject, the examination 

 of the alimentary matter of the Salpce opens up some new and 

 interesting facts, which prove the wide dispersion of numerous 

 minute organisms, both animal and vegetable, hitherto supposed 

 only to be found in shallow zones skirting the land. 



Having ascertained, with a certain degree of precision, the 



