WHITE CHALK COMPARED WITH CALCAREOUS OOZE. 531 
CHAPTER XLV. 
WHITE CHALK AS COMPARED WITH RECENT 
CALCAREOUS OOZES. 
In dealing with the Lower Chalk we ventured to compare its 
material with the calcareous oozes now being deposited in certain 
enclosed seas, such as the Gulf of Mexico. The Middle and Upper 
stages of the Chalk differ from the Lower in consisting of much 
purer material. A priori , therefore, it would seem natural to 
suppose that this purer material was formed in deeper w r ater 
and at a greater distance from land than that of the Low T er 
Chalk. This conclusion, however, has been disputed, and several 
eminent authorities have declared that no part of our Chalk 
formation is comparable with any modern oceanic deposit. 
It seems necessary, therefore, to discuss the general question 
of whether such a comparison can be made before we deal with 
special evidence regarding the conditions under which the Middle 
Chalk seems to have been accumulated. 
1. Points of Resemblance and Difference. 
Much has been written respecting the similarity between the 
material of the chalk and that of Grlobigerina ooze ; some have 
declared the resemblance to be very great, and have regarded 
“ the chalk ” as an ancient foraminiferal and oceanic deposit 
analogous to the G-lobigerina ooze now found on the Atlantic 
floor ; others (including Sir J. Murray) have pointed out certain 
marked differences between them, and have declared that they 
cannot have been formed under the same physical and geographi¬ 
cal conditions. 
It appears to me that this is a subject on which it is possible to 
take too wide and general a view on the one hand, or a too limited 
and restricted view on the other ; and that a really valid opinion 
can only be arrived at by careful steering between these two 
extremes, and by a more thorough consideration of the facts and 
possibilities than anyone has yet attempted. 
For instance, until about ten years ago most of the writers who 
discussed this question spoke of “ the chalk,” or “la craie,” as if 
its composition was similar throughout, utterly ignoring the 
existence of such beds as the Melbourn Rock and the hard beds 
which occur in the zone of Holaster planus ; to say nothing of the 
more minute differences which are observable by the aid of the 
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