17 
The Pre-Cambrian series of Pembrokeshire is divided by 
Dr. Hicks into three groups, which in descending order are 
named “ Pebidian,” ‘ Arvonian,” and ‘‘Dimetian.” These, 
which consist mainly of altered or metamorphic rocks, are 
wholly devoid of fossils. They are overlaid by the lowest 
“Cambrians” or “ Harlech Grits,” from which they are sepa- 
rated by a thick bed of conglomerate, which is deposited upon 
them uncomformably. This bed of conglomerate is shown to 
be persistent over great areas; it is described as of many feet 
in thickness, and as consisting of rolled materials of all sizes, 
shewing an ancient coast-line, with evidence of great disturb- 
ance. The Rev. W.S. Symonps writes—“ It is singular that 
this conglomerate bed should extend so widely at the base 
of the Cambrians. I have seen it away in the Hebrides, in 
Sutherland, and in S. Wales, and it occurs along the same line 
in the Malvern hills.” 
The underlying Pre-Cambrian beds have been so altered by 
heat and pressure, that it is only after long and intimate 
acquaintance, aided by patient research, that their sequence 
can be determined: indeed the conclusions of Dr. Hicks have 
not met with universal acceptance, many Geologists of the 
highest consideration continuing to regard these deposits as 
due to intrusive volcanic action. 
It is well known that in America and in the north of 
Scotland there exists a vast thickness of Pree-Cambrian rocks, 
known as the ‘“‘ Laurentian” series: these are regarded by Dr. 
Hicks as underlying the Pre-Cambrians of Pembrokeshire and 
Caernarvon, which he regards as the uppermost beds of the 
Laurentian series. The question is a very intricate one, and 
one rendered all the more difficult by the entire absence of all 
evidences of life, except in the Laurentians of America, where 
the Hozoon Canadense occurs; but the presence in these beds of 
lime and phosphates, both of which are constituents of animal 
life, is appealed to as evidence of the existence of living beings 
on the land and in the waters of that old primeval world. 
There was a discussion afterwards, in which Dr. Wricur, 
Mr. Lucy and others took part, having reference mainly to the 
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