1898] PROBABLE DEPTHS OF THE GAULT SEA 307 
In his book “ The building of the British Isles” (5), A. J. Jukes- 
Browne says with regard to this question, “The clays of the Lower 
Gault seem to have been deposited in a shallow sea of 50 to 70 
fathoms deep, which is about the depth of the sea between England 
and Ireland, while the fossils of the Upper Gault of Folkestone 
indicate a depth of 100 fathoms and upwards.” From the foramini- 
feral data for each zone of the Folkestone Gault to be referred to 
subsequently, we obtain a mean depth for the Lower Gault (Zones 
I.-VII. of Price) of 830 fathoms. In a similar way the Upper 
Gault (Zones [X.-XIII.) gives a mean depth of 866 fathoms. 
The following are the zones with their separate results and 
points of interest :— 
Zone I. The Green-sand seam at the base of the Gault——This is a 
dark-coloured argillaceous green-sand. The included fossils are much 
rolled and worn, and this particular deposit appears to have been 
subjected to the prolonged action of currents. The depth obtained 
by the evidence of the foraminifera of this bed appears somewhat 
great, but can be accounted for by the. fact of there being a later 
foraminiferal fauna present, besides the assemblage of glauconite casts. 
This mixed fauna also appears again in Zone XII. of the Gault 
(formerly referred to as Zone XI. green-sand seam). 
For Zone I. basal bed a possible depth of 750 fathoms is 
obtained. 
At this horizon a single example of Hormosina globulifera was 
found, and although usually occurring at greater depths, it is inter- 
esting to note that Dr Goés records it from a depth nearly corre- 
sponding with the determination given above. 
The samples of green-sand collected during the voyage of the 
‘Challenger’ were taken from depths less than 900 fathoms, the 
average being 449 fathoms. With regard to the hydrographical 
distribution of green muds and sands, Messrs Murray and Renard 
observe in the volume on “ Deep Sea Deposits,’ p. 240, that they 
“ would appear to form an interrupted band along many continental 
shores at the upper edge of the continental slope.” 
The usual sequence of the shallow to the deeper parts of the 
areas occupied by terrigenous deposits is in the order of green-sand 
(where conditions for its formation are favourable), green mud and 
blue mud. In the case of the Gault this was followed by a semi- 
pelagic deposit forming the grey marls of the Upper Gault. 
From the samples of green-sand obtained by the ‘ Challenger, 
one may refer, for comparison, to the green-sand, Station IV., 
between Cape St Vincent and Gibraltar, depth 600 fathoms. 
Zone I. 5 feet above the base—A dark clay, greenish when wet, 
bluish when dry. 
This is probably equivalent to the modern fine glauconitic muds, 
