96 EXPEDITION OF THE "CHALLENGER m 



" Although we have met with the same phenomenon so 

 frequently, that we were at length able to predict the nature of 

 the bottom from the depth of the soundings with absolute cer- 

 tainty for the Atlantic and the Southern Sea, we had, perhaps, 

 the best opportunity of observing it in our first section across 

 'tlie Atlantic, between Teneriffe and St. Thomas. The first four 

 stations on this section, at depths from 1,525 to 2,220 fathoms, 

 show Gluhigeriva ooze. From the last of these, which is about 

 300 miles from Teneriffe, the depth gradually increases to 2,740 

 fathoms at 500, and 2,950 fathoms at 750 miles from Teneriffe 

 The bottom in these two soundings might have been called 

 * grey ooze,' for although its nature has altered entirely from the 

 Glohigerina ooze, the red clay into which it is rapidly j)assing 

 still contains a considerable admixture of carbonate of lime. 



" The depth goes on increasing to a distance of 1,150 miles 

 from Teneriffe, when it reaches 3,150 fathoms ; there the clay 

 is pure and smooth, and contains scarcely a trace of lime. From 

 this great depth the bottom gradually rises, and, with decreas- 

 ing depth, the grey colour and the calcareous composition of the 

 ooze return. Three soundings in 2,050, 1,900, and 1,950 fathoms 

 on the ' Dolphin Rise ' gave highly characteristic examples of 

 the Glohigerina formation. Passing from the middle plateau of 

 the Atlantic into the western trough, with depths a little over 

 3,000 fathoms, the red clay returned in all its purity ; and our 

 last sounding, in 1,420 fathoms, before reaching Sombrero, 

 restored the Glohigerina ooze with its peculiar associated fauna. 



"This section shows also the wide extension and the vast 

 geological importance of the red clay formation. The total 

 distance from Teneriffe to Sombrero is about 2,700 miles. Pro- 

 ceeding from east to west, we have — 



About 80 miles of volcanic mud and sand. 



