356 ADDENDA. 



After still further examination he wrote : 



" The volcanic debris, as you predicted, does stretch well across 

 from where it was first noticed. It is present in all the deep 

 soundings up to 21 (lat. 52° 5", long. 16^ 5'),. which gave some 

 minute but very well characterized pumice-like fragments. In 

 Nos. 22 and 23" (both east of 15° 20^ W.), '' I have detected 

 nothing that I could positively declare to be of volcanic origin. 

 No. 22 gave for the heavy parts some fine quartz sand, with mi- 

 croscopic globules of iron pyrites, and. some bits of hornblende 

 and feldspar." 



The health of Professor Bailey is feeble, and on that account he 

 could attack these interesting specimens only now and then. But 

 on the 16th of October he reported, 



" On the back track: I tried No. 8 to-day, and being on the 

 look-out for pumice, found it on a mounted slide, where it has es- 

 caped my attention in my first experiments. I then dissolved a 

 new portion of material, and detected, without difficulty, several 

 pieces of undoubted pumice in the residue. By 'pumice' I mean 

 a nearly colorless volcanic glass, which has been distended by gas- 

 es, and shows vesicles, ridges, conduplications, etc., which only 

 such a body could show. 



" It is, then, a fixed fact that, from No. 8 (lat. 50° 2^ long. 38° 

 30^ on one side, up to No. 21 (lat. 52° b\ long. 16° 5^), inclusive, 

 on the other, we have the volcanic debris ! I looked at No. 7 (lat. 

 50° 3', long. 40° 26^) again, but could detect nothing that I felt 

 sure of as volcanic. In the marginal specimens, the volcanic mat- 

 ter is in small proportion, and may easily be overlooked ; but in 

 No. 14 (lat. 52° 26^ long. 27° 18^), it is so abundant and well 

 characterized that it can not be missed. 



"As you know all that is known about the great currents of 

 the ocean, you can, better than any one, make use of these ' Plu- 

 tonic tallies.' I Imd forgotten that the Gulf Stream sometimes 

 brushes the Azores. It is not necessarily from any active vol- 

 cano that these matters come. The washing away of ancient vol- 

 canic sands would give ' ocean dus.t' enough for our purposes. 

 This dust, however, is much heavier" (and would therefore sink 

 faster) "than the organic tallies I have been accustomed to look for." 



