214 MR. JTJKES-BROWNE AND PROF. HARRISON 



we consider that the foraminiferal marl at Codrington, the cal- 

 careous foraminiferal beds at the top of Bissex Hill, the calcareo- 

 siliceous marl at Chimborazo which contains some foraminifera, 

 the similar beds below the red clays on Mount Hillaby, and the 

 highly calcareous marl of Farley Hill above Cleland, are all on the 

 same horizon. If this is so, the white-earth group everywhere 

 shows the same gradual passage upwards from chalky foraminiferal 

 beds at the base to siliceous radiolarian earth, and again from this 

 back to chalky foraminiferal marl or limestone. Above these last are 

 the red and mottled clays, and finally the highest-grey earths and 

 volcanic muds of Mount Hillaby. 



We also recognize two horizons of brown gritty marl : one between 

 70 and 80 feet from the base, seen at Conset Bay and in cuttings 

 on the railway, at Bissex Hill and at Castle Grant ; the other at a 

 much higher horizon, as exposed in the road-cutting by Chimborazo. 

 Ihere are moreover two bands of grey pumiceous sand, one between 

 80 and 90 feet from the base, seen at Conset Gully and Castle Grant, 

 and another near Chimborazo and Mount Hillaby, nearly 100 feet 

 higher up in the series. 



There is another conclusion which may be fairly deduced from 

 the preceding stratigraphical observations, and that is with respect 

 to the layers of hard limestone which occur in certain localities at 

 the bottom of the Oceanic Series. "We think the facts clearly show 

 that these are portions of the chalky earths, which have been 

 locally converted into limestone through the infiltration of calcite by 

 water that has percolated through some length and depth of the 

 calcareous earths. 



Our observations on the beds in situ and our analyses of them 

 in the laboratory induce the belief that some of them have been 

 largely altered by the action of water, and that some of the more 

 siliceous varieties of the deposit have had their silica percentage 

 increased by the abstraction of the carbonate of lime which was 

 originally present. At Springfield, for instance, there is a small 

 outlier which consists wholly of siliceous earth, although the horizon 

 is that of the lower calcareo-siliceous earths. Wherever also 

 the Oceanic earths have been reached below the coral-rock, they 

 are always found to be more or less altered by the passage of 

 water. There are only three localities where solution and re 

 deposition of the organic silica seem to have taken place to any 

 extent, viz. Springfield, Cleland Hill, and Castle Grant, at all of 

 which a free passage of water takes place. 



§ 6. Detrital Deposits of intermediate date between the 

 Oceanic Series and the Coral-rocks. 



In 1890 Mr. E. Easton, C.E., sent us a set of specimens which 

 had been obtained from beneath the coral-rock area, some from 

 shafts and borings, and some from subterranean watercourses. Most 

 of them are earthy marls composed chiefly of inorganic materials ; but 



