468 
JOURNAL OP THE PLYMOUTH INSTITUTION. 
The most characteristic of the Post Glacial phenomena of Devon 
are ossiferous caverns, raised beaches, submarine forests. Plymouth 
has examples of the first and second. 
These submarine forests occur at various points of the coast, as 
near on the one hand as Blackpool, Dartmouth ; on the other, as 
Pentewan, St. Austell. They consist of beds underlying the 
present beaches, and extending an unknown distance seaward, 
partially up valleys landward, and composed of vegetable detritus, 
mixed with branches and trunks of trees, and occasionally 
containing stumps in situ. 
The ancient beaches, precisely similar in their general character- 
istics to the existing, occur at intervals along the coast at a height 
of some 30 feet above the present sea level. When they were 
washed by the waves, the land must have been 30 feet lower than 
now. When the forests flourished, it was at least 40 feet higher. 
All the indications prove that these changes of level were gradual 
and extensive. 
Anterior to the beaches are the ossiferous caverns, or rather 
their contents. Mr. Pengelly argues, from the conditions of the 
famous Windmill Hill Cavern, Brixham, that its filling preceded 
the forest era by a period sufficiently long to allow of the excava- 
tion of valleys 100 feet in depth. This is quite confirmed by our 
own local phenomena. I hope to be able to prove that the bone 
caverns of Oreston received their contents ere the gorge of the 
Laira was excavated.* 
The bone-bearing caverns of Devonshire are among the most 
interesting of its geological phenomena. The ossiferous caves of 
this locality are entitled to peculiar distinction. They were the 
first to direct attention to cavern researches in the county, and 
among the earliest investigated in England. The first of the 
series was discovered in 1816, while the famous cave in Kirkdale, 
to which Dr. Buckland directed so much attention, was not found 
until five years afterwards. I cannot deal adequately with this 
important branch of my subject in the space now at my disposal; 
but a full statement of all that has been written about the Oreston 
* Mr. Spence Bate, f.r.s., in his presidential address to the Devonshire 
Association in 1863, directed attention to evidences of some of the valleys 
of the lower lands on the south and west of Dartmoor having been filled 
with debris of the Dartmoor rocks to a height of 100 or 150 feet, and then 
re-excavated. 
