366 PROFESSOR J. W. JUDD. 



found to be going on in the relative proportions of the two carbonates, intermediate 

 samples were selected, and the results of their analyses interpolated. 



The chief conclusions arrived at from the analysis of samples taken from the Main 

 Boring are as follows : — In the first 50 feet of descent there is a gradual rise in the 

 percentage of magnesium carbonate up to 16 per cent., this maximum occurring at 

 depths of 15 and 25 feet, with a falling off between those depths to 12 per cent. 

 Although the exact depths of all the samples from Professor Sol las' two borings is 

 not given, yet there is a similar rise in the proportion of magnesium carbonate, 

 indicated between the same limits of deptlis in both of these borings. As the second 

 of Professor Sollas' borings is situated at a distance of more than a mile-and-a-quarter 

 from the Main Boring, it is evident that this rise of the magnesium carbonate 

 percentage in going downwards is not a mere local phenomenon, but occurs over a 

 considerable area in the atoll. 



From the depth of 25 feet in the Main Boring there is a gradual decline in the 

 proportion of the magnesium carbonate present, till 50 feet is reached, when only the 

 normal 1 to 5 per cent, of magnesium carbonate is present. This state of things 

 prevails to the depth of 637 feet, when a rapid rise in the magnesium carbonate 

 percentage again commences, and is continued till a depth of 658 feet is reached, when 

 the })roportion of magnesium to calcium carbonate has attained the limit of 40 to 

 60. This high percentage of 40 of magnesium carbonate is maintained with small 

 variations, and two important lnterru})tions, to be more closely particularised, quite to 

 the bottom of the boring at 1114|^ feet. 



Between 819 and 875 feet the proportion of magnesium carbonate declines, showing- 

 great variations, but reaches a minimum of 4*8 at 826 feet, and a second oiie of 20 '6 

 at 866 feet, with a maximum between them of 28 '5 at 855 feet. Again, between 1050 

 and 1 097 feet there occurs the second but less marked falling off in the percentage 

 of the magnesium carbonate. We have here minima of 26*63 at 1061 feet and 307 

 at 1080 feet, with a maximum between them of 39"4 at 1070 feet. 



It is specially noteworthy that while the proportion of magnesium carbonate rises 

 so high as to approximate to the quantity necessary to make the double carbonate, 

 dolomite, it never quite reaches that limit. The proportion of magnesium carbonate 

 in dolomite is 45*65 per cent., while the sample in which the highest percentage 

 of that suljstance was detected, at 950 feet deep, contained 43 per cent. As a rule, 

 however, the percentage of magnesium carbonate in this lower part of the bore-hole is 

 about 40, thus falling short by nearly 6 per cent, of the quantity required to form a 

 complete dolomite. 



3. Preparation of Samples for Analysis. 



All the cores brought from Funafuti, having been immersed in sea-water, were 

 found to retain small quantities of chlorides, sulphates, and other soluble salts. The 

 rock of the reef, so far as it was penetrated, was more or less cavernous and pervious 



