“In indicating the nature of the bottom on the charts, we came, from experience and without any theoretical considerations, to use three terms for soundings in deep water.  Two of these, Gl. oz. and r. cl., were very definite, and indicated strongly-marked formations, with apparently but few characters in common; but we frequently got soundings which we could not exactly call ‘Globigerina ooze’ or ‘red clay,’ and before we were fully aware of the nature of these, we were in the habit of indicating them as ‘grey ooze’ (gr. oz.) We now recognise the ‘grey ooze’ as an intermediate stage between the Globigerina ooze and the red clay; we find that on one side, as it were, of an ideal line, the red clay contains more and more of the material of the calcareous ooze, while on the other, the ooze is mixed with an increasing proportion of ‘red clay.’

“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 certainty for the Atlantic and the Southern Sea, we had, perhaps, the best opportunity of observing it in our first section across the Atlantic, between Teneriffe and St. Thomas.  The first four stations on this section, at depths from 1,525 to 2,220 fathoms, show Globigerina 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 Globigerina ooze, the red clay into which it is rapidly passing 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 decreasing 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 Globigerina 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 Globigerina 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.  Proceeding from east to west, we have—­

About 80 miles of volcanic mud and sand,
  " 350 " Globigerina ooze,
  " 1,050 " red clay,
  " 330 " Globigerina ooze,
  " 850 " red clay,
  " 40 " Globigerina ooze;