g to the middle subdivision.
The same group is probably represented in Corea and the Liao-tung by
the thick "Sinisian" formation of F. von Richthofen.

In _South America_ upper Cambrian rocks have been recorded from north
Argentina.

The Lower Cambrian has been found at various places in _South
Australia_; and in _Tasmania_ a thick series of strata appears to be
in part at least of Upper Cambrian age.

_General Physical Conditions in the Cambrian Period._--The Cambrian
rocks previously described are all such as would result from deposition,
in comparatively shallow seas, of the products of degradation of land
surfaces by the ordinary agents of denudation. Evidences of shallow
water conditions are abundant; very frequently on the bedding surfaces
of sandstones and other rocks we find cracks made by the sun's heat and
pittings caused by the showers that fell from the Cambrian sky, and
these records of the weather of this remote period are preserved as
sharply and clearly as those made only to-day on our tidal reaches.
Ripple marks and current bedding further point, to the shallowness of
the water at the places where the rocks were made.

No Cambrian rocks are such as would be formed in the abysses of the
sea--although the absence of well-developed eyes in the trilobites has
led some to assume that this condition was an indication that the
creatures lived in abyssal depths.

At the close of the pre-Cambrian, many of the deposits of that period
must have been elevated into regions of fairly high ground; this we may
assume from the nature of the Cambrian deposits which are mainly the
product of the denudation of such ground. Over the land areas thus
formed, the seas in Cambrian time gradually spread, laying down first
the series known as Lower Cambrian, then by further encroachment on the
land the wider spread Upper Cambrian deposits--in Europe, the middle
series is the most extensive. Consequently, Cambrian strata are usually
unconformable on older rocks.

During the general advance of the sea, local warpings of the crust may
have given rise to shallow lagoon or inland-lake conditions. The common
occurrence of red strata has been cited in support of this view.

Compared with some other periods, the Cambrian was free from extensive
volcanic disturbances, but in Wales and in Brittany the earlier portions
of this period were marked by voluminous outpourings; a condition that
was feebly reflected in centra