In the following table I have given my own measurements and compared them with those taken by Mr. Farrer.

[TABLE OF MEASUREMENTS.]

13th Mar. 1873.
Inches.
1839.
Inches.
30 Oct. 1845.
Inches.
Increase
since
Rate of Increase
per annum.
Inches.
1839.1845.
 1 Basal circumference at Gauges128    118  120   10  8  ·2941-·2857
 2 Gauge No. 1 to Gauge No. 2 52·625
 3 ” 2 ” 3 35·0  
 4 ” 3 ” 1 40·375
 5 Gauge No. 1 to hole in centre of basin at apex 30    
 6 ” 2 ” ” 29·5  
 7 ” 3 ” ” 31·4  
 8 Height from Gauge No. 1 20·9  
 9 ” ”2 min 20·4  
10 Maximum 29·7  
11 Tape measurement on slope
Gauge No. 1 to edge of apex
 26·7  
12 ” No. 2 ” ” 26·6   21·0  5·6
13 ” ” maximum ” 36·0   32·0 35·0  4·01·0 
14 Roof to apex of Jockey Cap 87      95·25 8·25·2946
15 Roof to tip of stalactite  10   
16 Stalactite to apex of Jockey Cap  85·25

Unfortunately I have been unable to identify the exact spots where the stalagmite was measured by Mr. Farrer, so that the only measurement which affords any trustworthy data for estimating the rate of increase is number 14. With regard to this, the only possible ground of error is the erosion of the general surface of the solid limestone, of which the roof is composed, by carbonic acid, since the year 1845, and this is so small as to be practically inappreciable. We have, therefore, evidence that the Jockey’s Cap is growing at the rate of ·2946 of an inch per annum, and that if the present rate of growth be continued it will finally arrive at the roof in about 295 years. But even this comparatively short lapse of time will probably be diminished by the growth of a pendent stalactite above, that is now being formed in place of that which measured ten inches in 1845, and has since been accidentally destroyed. It is very possible that the Jockey Cap may be the result not of the continuous but of the intermittent drip of water containing a variable quantity of carbonate of lime, and that, therefore, the present rate of growth is not a measure of its past or future condition. Its possible age in 1845 was estimated by Prof. Phillips at 259 years, on the supposition that the grain of carbonate of lime in each pint was deposited. If, however, it grew at its present rate it may be not more than 100 years old. All the stalagmites and stalactites in the Ingleborough Cave may not date further back than the time of Edward III. if the Jockey Cap be taken as a measure of the rate of deposition.


INDEX.

THE END.

LONDON: R. CLAY, SONS, AND TAYLOR, PRINTERS.