154 Mackhintosh—Brimham Rocks. 
Pacific coast. Several of these can scarcely have travelled through 
Behring Straits, not being Boreal forms. They have not been found 
in the British parallels, but appear in deep water off the Sta. Barbara 
group of islands; with other species not found on the continent, in 
the midst of the Lower Californian fauna, and in company with 
Tropical forms here finding their northern limit. 
These investigations are only just commenced. The results of the 
Californian Geological Survey are now under consideration ; and 
will doubtless bring to light many points of great interest on the 
connection between the ancient and the existing faunas. 
V. MARINE DENUDATION ILLUSTRATED BY THE BRiIMHAM ROCKS. 
By D. Macxintosu, F.G.S. 
HE claims of the sea as a denuding agent have been much dis-- 
puted of late years; the meteoric and fluviatile theories of 
denudation have been revived; and the glacial theory has been 
extended, so as to encroach on what was once generally admitted to 
be the legitimate province of the sea. But, as a forgetfulness of, as 
well as too much reliance on, the power of the sea to modify, may 
become a fertile source of hasty and false generalization, it is well 
that the importance of waves, tides, and currents, as denuding 
causes, should be re-asserted, and attention directed afresh to the 
more striking monuments they have left behind them in regions 
removed from their present theatre of action. ‘These monuments 
present an unmistakeable resemblance to the cliffs, buttresses, 
walled inlets, pillars, needles, &c., now in course of being formed by 
the sea ; and in explaining them, the old principle of sound theoriza- 
tion—similar effects are referable to similar causes—is not to he 
set aside by overstraining the capabilities of any theory which will 
merely account for the phenomena. Many of the appearances above 
mentioned have been attributed to atmospheric agency; and the 
denuding influence of air, rain, frost, &c. must to a certain extent 
be allowed. But the action of the atmosphere has not only been 
applied to the explanation of rocky scenery which is more obviously 
the result of oceanic denudation, but it has, I think, been extended 
to phenomena which the sea alone could have produced. Meteoric 
agents, generally speaking, operate from above, and their mechanical 
effects at least are confined to a decrease of level, or the formation 
of slight inequalities. If we except the chemical influence of air 
acting imperceptibly on rocks of a certain composition, meteoric 
agents are inadequate to the production of the following class of 
phenomena :—caves, with narrow entrances, and large amphitheatres 
within, indicating a laterally excavating agency, such as that of 
waves and tidal currents,—precipitous cliffs, with blocks of rock in 
positions, or presenting forms, which could only have been occasioned 
by the undermining action of the sea,—narrow inlets with vertical 
or overhanging walls,—pillars with slender pedestals,—rocks with 
nearly horizontal perforations,—and many other conditions which 
reveal not only a laterally extending, undermining, and even up- 
