part 3] mim:kw.s;\ cobal-limestoxes of Barbados. L59 



rarely fragments of a pyroxene. A few of my own slices also 

 indicate the presence of these minerals in the coral-rock. 



The source of the red argillaceous earths which form the soils 

 over the coral-limestones on the higher terraces (700 feet and 

 upwards) of the island lias lone,' been a matter of interest. The 

 red soil was described, and its origin pointed out by Jukes-Browne 

 and myself, on pages 50 to 53 of our little treatise entitled 'The 

 Geology of Barbados' I L890) in the following words: — 



' In the coral area the most remarkable soil is certainly the red clay or 

 loam which occurs on all the higher parts of the area. This is thickest on 

 the very highest plateau above 900 feet, below 80J feet it is much thinner, 

 and it does not reach below 500 feet ; indeed, between 500 and 700 feet it 

 becomes rather a yellow clay, and is in many places covered and concealed by 

 dark carbonaceous earth, the so-called " black soil : " which is black or brownish 

 black. 



' Where best developed, the red clay appears as an unctuous loamy clay of 

 a deep red colour, or more often variegated red, yellow, and brown, and 

 it bears a great resemblance to the red and mottled clays which are so fre- 

 quently found on the Chalk districts of Southern England. The average 

 thickness of this soil on the high ground is from 2 to 3 feet, but the surface 

 of the coral-rock is so very uneven that the depth of the soil varies in every 

 rds it fills up the hollows, and is "piped'' into the holes by which this 

 rock is honeycombed. Deep deposits of it are frequently found, and wells 

 are said to have been sunk 40, 50, and even in one case near Castle Grant 

 DO feet, without reaching the bottom of such clay-filled holes 



'With regard to the origin of the red soil, we have no doubt that it has 

 been produced by the gradual disintegration and solution of the coral-rock 

 itself. At first sight it seems hardly possible that the decay of a nearly pure 

 white limestone should result in the formation of a red clay, for the coral- 

 rock is almost entirely composed of carbonate of lime, with generally less 

 than 2 per cent, of silica and silicates, and only a minute quantity of oxide of 

 iron ; while the red soil contains about 60 per cent, of silica and silicates, 

 with 9 or 10 per cent, of iron oxide, and only some 2 per cent, of carbonate 

 of lime. 



' It is, however, a fact that wherever a limestone is exposed to the slow 

 solvent action of rain-water a similar red soil is produced, and Barbadians 

 need go no farther than San Domingo to find a case where this admits of 

 proof, for along the western part of the south coast of that island there are 

 raised coral-reefs covered by a similar red soil, and this soil is absolutely 

 confined to the coral areas. Again, in Jamaica a red soil occurs everywhere 

 over the surface of the white limestone which forms such a large part of that 

 island. 



' These red soils represent the residue of a great thickness of the limestone- 

 rock ; that is to say, they indicate the removal of a great thickness of the 

 rock, the pure carbonate of lime having been dissolved by the rain-water 

 which has fallen upon the surface, and has (lien run oil' or percolated through 

 to lower levels, while the small proportion of insoluble matter has been left 

 on the surf ace or swept into its hollows. This mode of origin explains Hi-' 

 fact of the red soil being thickest on the highest levels, tor it is these parts 

 which have been the longest above the level of the sea, and which have 

 therefore been exposed for the longest time to the action of the rain and the 

 weather. 



'Basing a calculation on the average amount of insoluble matter in the 

 coral-rock, we find that from 50 to 60 cubic feet of such rock must have been 

 destroyed in order to produce 1 cubic foot of the red clay. ami. if we could 

 ascertain the rate at which the destruction of the rock took place undei 

 natural conditions, we should have a basis for calculating how long it is since 

 Barbados first rose above the waves.' 



