na.

"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;

giving a total of 1,900 miles of red clay to 720 miles of _Globigerina_
ooze.

"The nature and origin of this vast deposit of clay is a question of the
very greatest interest; and although I think there can be no doubt that
it is in the main solved, yet some matters of detail are still involved
in difficulty. My first impression was that it might be the most minutely
divided material, the ultimate sediment produced by the disintegration of
the land, by rivers and by the action of the sea on exposed coasts, and
held in suspension and distributed by ocean currents, and only making
itself manifest in places unoccupied by the _Globigerina_ ooze. Several
circumstances seemed, however, to negative this mode of origin. The
formation seemed too uniform: wherever we met with it, it had the same
character, and it only varied in composition in containing less or more
carbonate of lime.

"Again, the were gradually becoming more and more convinced that all the
important elements of the _Globigerina_ ooze lived on the surface, and it
seemed evident that, so long as the condition on the surface remained the
same, no alteration of contour at the bottom could possibly prevent its
accumulation; and the surface conditions in the Mid-Atlantic were very
uniform, a moderate current of a very equal temperature passing
continuously over elevations and depressions, and everywhere yielding to
the tow-net the ooze-forming _Foraminifera_ in the same proportion. The
Mid-Atlantic swarms with pelagic _Mollusca_, and, in moderate depths, the
shells of these are constantly mixed with the _Globigerina_ ooze,
sometimes in number sufficient to make up a considerable portion of its
bulk. It is clear that these shells must fall in equal numbers upon the
red clay, but scarcely a trace of one of them is ever brought up by the
dredge on the red clay area. It might be possible to explain the absence
of shell-secreting animals living on the bottom, on the supposition that
the nature of the deposit was injuri