8 Proceedings of the Royal Physical Society. 
We have, however, on the contrary, every reason to believe 
that they have been covered by many thousands of feet of 
marine sediments, which have now been worn away. The 
present exposures, in fact, are probably the result of the 
long-continued denudation of great mountain chains—them- 
selves, perhaps, of comparatively recent date; and they do 
not necessarily indicate anything as to the form and trend of 
the original continents. On the other hand, judging from 
the numerous isolated inliers of Archean rocks in districts 
remote from the main exposures, it seems probable that an . 
Archean platform constitutes everywhere the floor upon 
which the post-Archeean sediments were laid down. 
If we may be permitted to speculate, it would seem prob- 
able that at the commencement of Cambrian time the 
European area was occupied by a shallow ocean, studded 
here and there with larger or smaller masses of Archzean 
land—the condition, in fact, being that of an archipelago. 
We have at present no definite evidence of the existence in 
the European area during Cambrian times of deep-water 
conditions ; but it does not follow that such conditions did 
not exist elsewhere in regions which have not yet been 
thoroughly investigated, or which are concealed beneath the 
waters of our present oceans. Similarly, we have not at 
present definite evidence of the existence during Cambrian 
times of any large mass of continental land in either the 
European or the North American areas. Nevertheless, there 
is every reason for agreeing with Neumayr when he remarks 
(“ Hrdgeschichte”) that the proof that continents existed in 
Cambrian, and even in Archean, time is “so clear and con- 
vincing that it is hardly intelligible how anyone could have 
arrived at a different conclusion.” 
There is not, in fact, sufficient evidence at present avail- 
able to compel the acceptance of the sweeping generalisation 
that throughout Paleozic time the ocean was more uniform 
in depth and temperature than it is at present, and that the 
land-masses were small and distributed throughout an all 
but universal sea. The argument which has been principally 
relied upon in support of this contention, is that the succes- 
sive systems of the older Paleeozoic rocks contain a shallow- 
