1898] PROBABLE DEPTHS OE THE GAULT SEA 311 



It has already been pointed out that those authors who have 

 expressed any opinion as to the depth of the Gault Sea have not 

 given anything like the depths shown by these results based upon a 

 systematic inquiry into the distribution of the foraniinifera through- 

 out the Gault at Folkestone (2). Previous authors, with the exception 

 of Professors Parker and Jones, 1 have based their results upon data 

 a Horded by a consideration of the groups of the mollusca, Crustacea, 

 and other of the larger organisms. These higher groups from 

 modern deposits have, in many cases, only been specially dredged 

 from moderately shallow depths. Although the bathymetrical range 

 of these larger forms is in most cases rather limited to the shallower 

 parts of the ocean, it appears to me extremely probable that current 

 action, of which there is abundant proof throughout the Gault at 

 Folkestone, has there operated in bringing together assemblages of 

 testaceous remains from the higher continental slope on which they 

 flourished, to greater depths where these accumulations took place. 

 It is more reasonable to imagine the removal of the shallow' forms 

 to deeper areas than to suppose that the finer muds with foraniini- 

 fera could be brought into shallower waters. 



The presence of phosphatic nodules, so abundant in the Gault, 

 by no means indicates shallow water. That these are due to currents, 

 and by the changes of temperature consecpuent on their inter- 

 mingling, has been clearly shown by Murray and Eenard (" Deep Sea 

 Deposits," p. 397), who state that phosphatic concretions "may be 

 found in all terrigenous deposits, and also along the edge of the 

 abyssal zone in deposits of a pelagic type, which, however, from 

 their nearness to land, still contain terrigenous elements." These 

 authors also point out (p. 396) "that phosphatic nodules are 

 apparently more abundant in the deposits along coasts where there 

 are great and rapid changes of temperature, arising from the meeting 

 of cold and warm currents, as, for instance, off the Cape of Good 

 Hope and off the eastern coast of North America. It seems highly 

 probable that in these places large numbers of pelagic organisms are 

 frequently killed by these changes of temperature, and may in some 

 instances form a considerable layer of decomposing matter on the 

 bottom of the ocean." 



That current action played an important part during the deposi- 

 tion of the Gault is, therefore, not only proved by the numerous 

 lines of phosphatic concretions found at certain intervals, but also 

 by the presence of green-sand seams and scattered gla aconite grains 

 found throughout the formations. 



The depths here given for each zone of the Gault are merely 

 recorded for what they may be worth ; for after all it is a result 



1 Professor Rupert Jones has already expressed to me his belief that the calculation 

 made many years ago by him and his colleague Parker is probably of far less depth than 

 it should be. 



