382 ON THE FAUNA AND BOTTOM-DEPOSITS NEAR THE 30-FM. LINE 



grailes G'3 and 7"0, the lower numbers corresponding to the coarser and the 

 higher to tlie finer textures. 



"Grade VII.— the 'fine sand' — varies considerably in the different samples. 

 Its coarser forms approximate in some few samples to a sand the individual 

 grains of which are none greatly under "5 mm. in diameter. Its finer forms 

 in some samples have but few grains of these dimensions, as compared with 

 a great number of grains approximating to the ' silt.' 



" 2. Carbonate of Lime. — Care was taken to ascertain how far any results 

 of chemical determination might be invalidated by the presence of inorganic 

 carbonate of lime in the rock fragments. The result of inquiry proved that 

 practically no lime existed in the rock fragments which was soluble in cold 

 dilute hydrochloric acid. All carbonate of lime so soluble is in these samples 

 of organic origin. 



" In the finer grades below III. carbonate of lime was determined by treat- 

 ing each sample with dilute hydrochloric acid, filtering, neutralising the filtrate 

 with ammonia and again filtering, precipitating the lime with ammonium 

 carbonate [(NH^)oC03], filtering, washing precipitate, drying and weighing 

 as carbonate of lime. 



"In grades I., II., and III. the shells, shell fragments, etc., were picked out 

 by hand and weighed. 



"Tables III. and IV., p. 526, give the results thus obtained. 



" A feature of these results is the low percentage of CaCog in the fine 

 texture deposits, having an average grade of 6"4 to 7 0. In Table V., p. 528, the 

 samples are arranged in order of their average textures and the total percentage 

 of CaCog set opposite each sample. 



" The coarse samples are not, perhaps, uniformly high in their percentage of 

 carbonate (94 is a notable exception), nor are the fine samples uniformly low, 

 89 B and 109 being the exceptions, but on averages the general figure for the fine 

 textures falls much below that for the coarse. Another noticeable fact is that 

 the percentage of carbonate of lime found in the finer sands of each sample 

 shows a distinct tendency to follow the total amount of carbonate of lime 

 present in the gravel and coarse sand of the same samples (again with the 

 exceptions of 89B and 109, which are evidently detrital matter from adjacent 

 shelly grounds). 



" This points to the fact that most of the carbonate of lime in the fine sands 

 is detrital matter from shell fragments, etc., in the gravels and coarse sands, 

 and microscopic examination confirms this. 



"The percentage of carbonate of lime in the silts is comparatively low, with 

 the exception of silt 109. It apparently follows no definite rule, beyond 

 a mere tendency to be somewhat higher in silts where the whole sample 

 is rich. There is less variation between different samples in the matter of 

 percentage of carbonate of lime in the silts than in any other feature, 



" An attempt might be made to explain the poverty of the silts in carbonate 

 by the fact that once shell fragments are ground sufficiently fine to pass into 

 this grade they present so much surface area in proportion to their solid 

 capacity as to fall an easy prey to the solvent action of sea-water. 



