180 MR. JUKES-BROWXE AND PROF. HARRISON 



presence of angular mineral chips or grains, and of more minute in- 

 organic particles which differ from those usually met with in our 

 Chalk ; 6, in the larger proportion of the minuter particles which 

 can be resolved by high powers and are directly suggestive of deri- 

 vation from foraminifera, siliceous organisms, ooccoliths or crystal- 

 loids. These particles present a different appearance from that of 

 the minute crystals of calcite which occur in the English Chalk. 



As in the English Chalk, the perfect or nearly perfect tests of 

 foraminifera occupy a small area when seen in sections. 



Comparison with the "White Limestone of Jamaica. — 

 As mentioned in a former report by Mr. Hill, certain parts of the 

 AVhite Limestone of Jamaica appear to be of oceanic origin. 



A specimen obtained from Hanover County was kindly sent me 

 by Col. Eeilden, and another, already mounted as a microscope 

 slide by Messrs. Watson, has been obtained for comparison. 



Both agree very closely with the calcareo-siliceous section of the 

 Barbados Oceanic Deposits. The specimen sent by Col. Eeilden is 

 harder and more crystalline than many of the oceanic ' earths,' but 

 will compare in this respect with the siliceous limestone at the base 

 of Cleland Hill. Thick-shelled Glohic/erina?, similar to those of 

 the Barbados rocks, are conspicuously abundant, and one or two 

 radiolarians can be seen in outline. 



(4) Pumiceous Earths. — Miss E-aisin reports that these con- 

 tain very few organisms and consist mainly of volcanic materials, 

 the particles of which vary from -05 to over 1 mm. india meter. 



(1) Castle Grant, middle gritty beds. 



(2) Melviii's Hill, a light grey, slightly coherent sand. 



In the first specimen the mineral chips are mostly felspar, often 

 in broken crystals and exhibiting multiple twinning, but there are 

 numerous flakes of clear pumiceous glass, and two or three large 

 pieces of mica. The groundmass consists of fine argillaceous 

 material. 



The second consists mainly of flakes and splinters of clear colour- 

 less pumice, many of these exhibiting the usual vesicular structure 

 with rounded ar ' pipy ' cavities. There are a few chips which 

 appear to be felspar, occasionally twinned and often broken crystals. 

 Some radiolarian tests also occur. 



(5) Grey Mndstones. — These were examined by Miss Eaisin. 



(1) Mount Hillaby, 10 feet from top of northern peak. 



(2) do. 5 feet do. do. do. 



In the above specimens a gelatinous or argillaceous substance 

 forms the groundmass, in which are scattered small, angular mineral- 

 fragments and a few radiolaria, but there is no calcareous matter. 

 Many of the minerals are broken crystals, and they suggest the 

 characters of fine volcanic dust. 



In the first some particles are probably felspar, some may be 

 mica, and there is one rather large grain, somewhat rounded, which 

 is probably quartz (diam. 1 mm.). 



In the second the particles are chiefly angular, but include a few 



