IV DEPTHS AND DEPOSITS OF THE OCEAiN 205 



with any known rock of this type in the North Atlantic basin. The 

 lava - form and intrusive types of the basic materials have marked 

 affinities with the tertiary volcanic rocks of the Inner Hebrides and the 

 north of Ireland. 



Of special interest is the evidence pointing to the conclusion that the 

 rock fragments from this station must have been transported by floating 

 ice during some phase of the glacial period. More than half of the 

 specimens are glaciated, the larger part of the remainder are angular, 

 and a number are well rounded. A typical example of one of the 

 glaciated stones is shown in Fig. 145, which is a portion of a larger boulder 

 broken off before being embedded. Irregular striae appear on this 

 specimen, but on one surface it is facetted and the striae thereon |are 

 more or less parallel. It is noteworthy that the glaciated and ice- 



FiG. 147. — Surface of Specimen No. 4 in Fic. 146, enlarged to show 

 " Chatter-marks." 



moulded specimens include nearly every rock type represented in the 

 collection from this particular station. The stones resemble those found 

 in boulder clay or " moraine profonde," indeed in some instances the 

 clayey matrix of this deposit has been cemented to some of them by 

 calcareous matter. 



Some of the rounded specimens, consisting of Silurian greywackes, 

 carboniferous limestone, chalk -flint, dolomite, and vein - quartz, are 

 shown in Fig. 146. These must have been rounded before they reached 

 the position from which they were dredged. 



An enlarged part of specimen No. 4 in Fig. 146 (chalk-flint) is repre- 

 sented in Fig. 147, to illustrate the bulbs of percussion or " chatter-marks " 

 which it displays. Such evidence indicates that the stones had originally 

 been dashed against each other by torrent or wave action, 



A careful examination of the specimens points to the conclusion that 

 all had been partially embedded in a Globigerina ooze on the sea-floor. 



