ON THE GEOLOGY OF BAKBADOS. 209 



farther up the hill a little of the fine soft red clay comes in between 

 the white earth and the coral, showing these to be the highest white 

 earths, though they are here 300 feet lower than their level at Cane- 

 field. 



Mount Hillaby.—A.s already stated on p. 202, the greater part of 

 the Hillaby area lies between two nearly parallel faults with up- 

 throws to the north, the beds themselves dipping to the N.N.W. ; 

 but the highest part of Mount Hillaby seems to be a faulted trough, 

 which not only forms the highest ridge in Barbados, but contains a 

 greater thickness of the Oceanic Series than is elsewhere preserved. 



We found that an ascent from near Airy Cot, on the south side of 

 the hill, gave us the best clue to its structure. -Just north of the 

 Schoolhouse, on the road to Airy Cot, a fault brings up the Scotland 

 Sandstones, and Airy Got Mill stands on them. North of and close 

 by the Mill the chalky basal beds of the Oceanic Series come in at a 

 level of about 905 feet, and they extend up the slope to about 940 

 feet ; then come white siliceous earths with a moderate proportion 

 of carbonates, passing up into purer siliceous earths which reach to 

 about 1040 feet, with a KN.W. dip; they must be over 100 feet in 

 thickness. Above are siliceous beds with some calcareous matter 

 reaching to 1070 feet, at which height an exposure shows four layers 

 of grey felspathic and pumiceous grit alternating with layers of white 

 radiolarian earth ; the gritty layers vary from 6 inches to 2| feet 

 in thickness, and the depth of the exposure is about 9 feet, 

 while the dip is about 8° J^.N.W. 



Above these come thick blocky beds- of tough calcareous earth 

 having the aspect of chalk, and these continue to the top of the 

 southern peak at a height of 1095 feet. We took samples from this 

 summit and from points at 5, 10, 20, and 30 feet below it. In some 

 of these buff-coloured pipings occur, and small lumps of limonitic 

 oxide of iron are not unfrequent here and elsewhere. 



On the next peak to the north-east these chalky beds are covered 

 by red and pink soft argillaceous earths like those of Castle Grant, 

 and these also dip to the N.N.W. A sudden change of dip then 

 takes place, owing doubtless to a fault, and the beds north-east of 

 its course dip eastward. The northern parts of the hill show red 

 earths dipping first E.S.E. and then east, and the path up to the 

 highest peak (1 104 feet) shows the top of these red clays dipping 

 S.S.E. at about 60° and succeeded by some 25 feet of grey siliceous 

 volcanic muds, the lower beds being finely laminated in dark and 

 light grey layers, and including a layer of fine whitish clay about a 

 foot thick. The highest beds are firm and blocky. 



The same volcanic muds are found on the north-eastern peak, 

 dipping E.S.E. at about 15°. The material of these beds is fine and 

 firm, and sufficiently hard to be used locally for walling purposes, but 

 near the top there is a thin layer (1| inch) of coarse felspathic grit. 



Passing westward and recrossing the line of fault, we came upon 

 a mass of coloured clays, red, pink, yellow, and white, dipping as 

 before to the JST.jS'.W., but at a higher angle (about 40°), and a 

 thickness of at least 50 feet of them could be measured. 



