i 



ON TEE GEOLOGY OF J5AEBAD0S. 181 



pieces of pumice and some brownish spheres, which may have 

 resulted from the alteration of glauconitic casts of foraminifera. 



(6) Fine Clays. — These are the argillaceous earths mentioned 

 on p. 171 as similar to modern oceanic ' red clays.' 



(1) Hillaby estate, a pale yellow earth. 



(2) Castle Grant, a pink earth. 



(3) Canefield, a red earth. 



Miss Raisin reports that these consist mainly of a fine amor- 

 phous argillaceous substance, in which are some very minute 

 mineral fragments (-005 to -030 mm. in diameter) ; organisms are 

 scarce, but occasionally a spicule, a broken radiolarian test, or a 

 foraminiferal cast (-025 mm. or less) is seen. 



The mineral fragments can seldom be identified, but the general 

 form of many is suggestive of felspar. They are mostly angular and 

 often mere crystal-shaped specks. In the Canefield and Hillaby 

 earths are some small particles of an opaque metallic oxide (probably 

 black oxide of iron) with an aggregate and somewhat crystal-like 

 form, as if developed in situ. 



General Remarks on the Inorganic Constituents of Groups 4, 5, 

 and 6. — With reference to the pumiceous earths (4) and the grey 

 mudstones (5), Miss liaisin observes that the general appearance 

 of the mineral fragments in these rocks agrees very well with the 

 idea of a volcanic origin. They are seldom rounded, but generally 

 quite angular, and consist of broken chips of fresh-looking minerals. 

 Except that they are smaller, they are not unlike the particles in 

 the fine felspathic dust erupted from Cotopaxi,^ and those of the 

 volcanic dust which fell on Barbados in May 1812.^ The latter, 

 however, includes a fair amount of pale greenish pyroxene. Pumice, 

 too, is much more abundant in some of the Barbados rocks. 



It would appear that the falls of felspathic and pumiceous dust 

 sank through the water and mingled with the oozes which were 

 accumulating on the ocean-floor. 



The fine-grained coloured clays or argillaceous earths were com- 

 pared with two samples of 'red clay' from the Atlantic, but 

 unfortunately neither of these were pure ' red clays,' both samples 

 containing much calcareous matter. 



One of them (from lat. 24° 20' N., long 24° 28' W., 2740 fathoms, 

 supplied by Dr. J. Murray) is very calcareous ; ^ fragments of shell, 

 foraminifera, and apparently coccoliths occur, with one or two 

 rhombohedral particles bearing some resemblance to the rhombo- 

 hedral calcite of Bissex Hill. This deposit has many angular 

 crystalline fragments often too minute to be identified with cer- 

 tainty, but doubtless in many cases felspar; it has also indefinite 



^ Slides of this dust were kindly lent by Prof. Bonney. 



- A sample of this fall of dust was supplied by Prof. Harrison. 



^ [It appears from the account given of this sample in Dr. Murray's Report 

 on the Deep-eea Deposits that it was one from which all the finest .silty part of 

 the material had been previously washed away, leaving a residue which was far 

 richer in carbonate of lime than the original deposit. It was not therefore 

 suitable for our purpose. — A. J. J.-B., March 2l6t, 1892.] 



