512 Notices of Memoirs—W. H. Hudleston— 
position between the calcareous-volcanic Devonians of the South and 
the coarse quartzose sediments of the Welsh border, altogether 
devoid of mollusca. If we regard the “Old-Red” of South Wales 
as an inshore deposit over an area which was deluged with fresh 
water from off the land, we can believe that further out to sea, in the 
times of the Lower Old-Red, conditions were favourable for a 
moderate amount of marine mollusca. This does away with the 
necessity for a barrier, and also, in a general sense, it suggests a 
kind of gradation between the Old-Red, the North Devon, and 
the South Devon deposits. 
Bott Rocks, ETc. 
The age of the crystalline schists of the Bolt.—Besides the mere 
chronology of the subject, there are questions of considerable interest 
in connection with these schists, the consideration of which more or 
less involves the physical history of the bed of this part of the 
Channel, as well as of the adjacent lands. In this connection also 
we may endeavour more especially to review the physical structure 
of the entire South-west, to which allusion has already been made in 
reference to the effects of the great post-Carboniferous disturbance 
so obvious throughout Devonshire. 
The subject generally is by no means ripe for final deeitony and 
even if we limit our observations, in the first instance, to the Bolt 
Rocks and their submarine connections, real or supposed, we must 
allow that, if metamorphism has usually proved an obscure question, 
the study of metamorphism under water is hampered with additional 
difficulties. ‘There are no rocks in the county whose age and origin, 
even to this day, are so much debated as those which, speaking 
generally, we may term the Bolt Rocks. 
Of the numerous theories which have been advanced, the most 
doubtful, it seems to me, is that which regards the mass as the 
result of progressive metamorphism from the action of underlying 
or contiguous submarine granite. Allowing, for the sake of the 
argument, that there is progressive metamorphism, although Prof. 
Bonney and Miss Raisin distinctly deny it, there is very little in 
the chlorite- and mica-schists of the Bolt district which resembles 
the peculiar fringe of partially metamorphic rock due to contact 
with a granitic mass. Such fringes are usually marked by abundance 
of andalusite, amongst their other characteristics, especially when 
slates are invaded. Yet we do not hear of this mineral in connec- 
tion with the Bolt Rocks, though it must be admitted that the micro- 
scope has revealed the existence of kyanite, hitherto unsuspected. 
Let us now for a moment examine the case for progressive 
metamorphism, which has found a recent advocate in Mr. Somervail. 
Many of us perhaps, in common with that gentleman, fail to under- 
stand why all metamorphic rocks, not absolutely the result of contact 
action, should be claimed as Archean. But this unwillingness to 
accept their Archean age does not compel us to believe that there 
has been progressive metamorphism, whereby an extension of the 
Dartmouth Slates, even with the addition of interbedded igneous 
rocks, has yielded, under peculiar circumstances, the mica-schists 
and chlorite-rocks of the Bolt. Mr. Somervail’s argument, that the 
