MALTESE CAVES. 257 



Now the work TJ expended in the penetration of a plate by a force vary- 

 ing as the depth of penetration is expressed by the formula 



U=!Px T V; 



.-. ~U = Crf, (1) 



where the work requisite to penetrate a plate varies as the square of its thickness 



nmltiplied by the radius of the shot. 



Substituting the value of the constant C, deduced from the experiments 



with ordnance, we get 



U=24400jA (2) 



w v 

 where TJ= t - — , the work in the projectile at the instant of impact. 



Hence we have for the depth of penetration by a shot with a given weight, 

 size, and velocity, 



(3) 



-v; 



24400? 



From this formula it follows that a 100 lb. steel shot of tough temper, 6 

 inches diameter, with the velocity of 1200 feet per second, will completely 

 perforate an armour-plate 5 inches in thickness. This result is fairly borne 

 out by the results of experiments with ordnance. 



If 3f inches be taken as the average radius of a shot, then formula. (3) 

 becomes 



*«-*foV& (4) 



which may be regarded as a rough approximation of the damaging effect of 

 shot not differing widely from this dimension. 



Maltese Caves. — Report on Mnaidra Cave. 

 By A. Leith Adams, M.A., M.B., F.G.S. 



1. The strata composing the Maltese Islands belong to an early Miocene 

 period ; and attain a maximum height of about 720 feet above the sea-level. 

 They consist, from above downwards, of the Upper Limestone, underlaid by 

 beds of Sand, Marl, Calcareous Sandstone, and last of all, a rather compact 

 and durable rock called the Lower Limestone. The latter attains its greatest 

 height on the south and south-west coasts, reaching an elevation of 300 feet 

 above the sea-level. Several cliffs of this bed contain natural caves, one of 

 which, the subject of this Report, was discovered by me in 1863. 



2. The Maltese strata are all more or less displaced by faults, whilst their 

 exposed surfaces well attest the denuding effects of bygone atmospheric and 

 aqueous agencies. This is very apparent in many situations ; indeed the 

 generally bare aspect of the islands, and the accumulations of soil and frag- 

 ments of rocks in the fissures and hollows, together with depressions existing 

 here and there, fully testify to the great changes which the area underwent 

 during and subsequently to the period or periods when the remains of its post- 

 tertiary fauna were being buried in those situations. 



3. The alluvial deposits of the Maltese Islands consist — 1st, of a calcareous 

 red clay, containing peroxide of iron, and similar to that of many of the other 

 islands and along the shores of the Mediterranean ; and 2ndly, a blue marl, 

 which is obtained from the degradation of the bed of that name, found in situ 



1865. t 



