88 
JOURNAL OF THE PLYMOUTH INSTITUTION. 
Devon, here at Oreston, and illustrated most cogently by the reve- 
lations of Kent's Hole and Brixham. But we have lost much. 
Long before they attracted scientific notice, and in too many cases 
since, the contents of bone caverns met with no better fate than 
that of being turned to road-mending, thrown into limekilns, or 
sold at so much per pound to the marine store dealer. 
Because our district holds such an important relation to this 
branch of science, and because the latest bone cavern of the locality 
came under my own investigation, I have been led to direct attention 
to this subject. Nearly all that had been written about the Oreston 
caves up to 1872, was published by Mr. Pengelly, f.r.s., f.g.s., 
in the Transactions of the Devonshire Association for that year ;* 
but the Oreston, though the principal, are not the only ossiferous 
deposits of the Plymouth limestone ; and it is my present aim to 
present a complete consecutive history of all the bone caves of 
Plymouth, including therein my own observations. 
The Plymouth limestone forms a band averaging above half a 
mile in width, and extending six miles from the Dockyard on the 
west to West Sherford on the east. It has an average height of 
one hundred feet above mean sea level ; and its beds have a general 
southerly dip. A more constant feature than its bedding is the 
regularity of its divisional planes, those approximately perpendicular 
joints or divisions which cut the rock at right angles to the bedding 
in two great series, in a northerly and southerly, and easterly and 
westerly direction, and may be seen traversing the face of the 
quarries from top to bottom. These planes are the result of causes 
subsequent to the formation of the rock, which, with the aid of 
the bedding, they break into rhomboidal masses, suggesting a rude 
kind of crystallization. In these joints the caverns originate. 
Water charged with carbonic acid exercises a chemically solvent 
power over limestone. Finding its way into the joints from the 
surface, it eats away by slow degrees the rock-faces exposed to its 
action. Hence the caves. Give the water time, and it will work 
wonders. When the water is overcharged with lime redeposition 
is set up, and stalactite and stalagmite result. Where the under- 
ground current is most persistent and extensive there most work 
will be done. The caverns commonly run with the joints and 
across the bedding. At one point of Cattedown, and again imme- 
diately opposite at Oreston, there is a continuous line of cavities 
* Vol. v. part i , pp. 249-316. 
