How is the Cambrian divided 2 ATT 
ing of the Menevian fauna in South Wales by Dr. Hicks. 
In the process of elaborating the Cambrian faunas, the 
first step was the discrimination of the two faunas in the 
Lingula flags in 1853. h 
1865. In this year Messrs. Salter and Hicks made known 
the Menevian fauna, and showed the position of 
the Paradoxides beds in Britain. 
1866. In this year the Tremadoc fauna was distinguished 
in South Wales, and fully confirmed in 1872. 
1869. In 1869 Messrs. Hicks and Harkness described the 
great series of red, green and grey slates below 
the Menevian in South Wales, and showed the 
existence of a fauna older than that of the 
Paradoxides beds but with no trilobites. 
Subsequently Dr. Hicks elaborated the Cambrian system 
into seven groups, but showing only four trilobite faunas, 
the first or oldest not having been found by him in Britain. 
The groups of sediments containing these faunas he classi- 
fied as follows: 
Lower Cambrian. Three groups.—Caerfai, Solva and 
Menevian. 
Upper Cambrian. Four groups.—Maentwrog, Ffestiniog, 
Dolgelly and Tremadoc. 
It may be well to inquire what there is to support this 
classification of the Cambrian system, before adopting a 
new one. 
Two principal criteria for determining a question of this 
kind would be the facies and succession of the faunas and 
the bulk of the measures. In applying these tests, we turn 
our attention first to Scandinavia, for in no part of the 
world is there known such a clear, continuous and complete 
succession of Cambrian faunas as in that country. 
Connection, etc., of the Cambrian faunas. 
Of the several classes of organisms of these faunas, the 
trilobites may be taken as the group which will best show 
the relationship subsisting between the several faunas, for 
