NO. U.] MECHANICAL COMPOSITION OF SAMPLES. 13 



region where a comparatively large quantity of material is carried out from 

 the land. It has been proved that since the Glacial Period there have been 

 several alternate periods of drier and moister climate. The greater the 

 precipitation, the greater is the erosion and the consequent deposit upon the 

 sea-bottom, of terrigenous matter; and thus in a moister period, the grey clay 

 will extend farther out into the sea. If we had a vertical section of the 

 ocean-bed, we should see that wedges of the grey and the brown clay 

 alternate with one another just as many times as there have been climatic 

 periods. 



Sample No. 10 of the Fram Expedition consists, unlike those from the 

 other localities, of clay greyish above, brownish underneath. Here the pos- 

 sibility of a separation brought about by movement seems to be excluded, 

 especially as the two kinds of clay have an equally large admixture of sand. 

 It may be imagined that there was temporarily a rather considerable de- 

 position of sediment at this particular spot as compared with what there had 

 previously been ; but as long as nothing is known of the climatic changes in 

 these regions, there is nothing on which to base a conclusion as to the reason 

 for this. On comparing the two kinds of clay, it appears that the sedimen- 

 tation must take place two or three times as rapidly now as formerly. Strange 

 to say, the chemical analysis of these two samples shows no corresponding 

 difference in the proportion between the quantities of protoxide and peroxide 

 of iron. The grey clay contains 2*40 and 530 per cent respectively, while 

 the brown clay has 2 - 95 and 5-25 per cent; but this must be due to chance 

 causes, possibly some difference in the mineral contents. 



No chart of the distribution of the various kinds of bottom-samples ac- 

 companies the treatise, nor could one be drawn up with any great accuracy. 

 The boundary between the shallow water deposits and the Grey Deep-Sea 

 Clay, is placed, as already mentioned, at the 200 metres contour, and is thus 

 not directly connected with the nature of the bottom-sample. Throughout the 

 whole region, the only deep-sea deposit found is the Grey Deep-Sea Clay, a 

 name that is not altogether appropriate, as it also includes several rather 

 distinctly brown deposits. The boundary between this species of clay and 

 Globigerina Ooze is placed at 30 per cent carbonate of lime in the report of 

 the Challenger Expedition. If, following Schmelck, we make a special class 

 under the name Transition Clay, some of the most northerly samples might 



