286 EMMERICH ON THE MORPHOLOGY, CLASSIFICATION ; 
turbed in the highest degree. It is owing to these causes that 
it has hitherto been impossible to separate it into subdivisions. 
The fossils, which Portlock describes and figures from these 
strata, evidently belong to the three lower systems of the trans- 
ition rocks, to the two Silurian and to the Devonian. To confine 
ourselves, however, to the Trilobites, Portlock enumerates the 
following belonging here :—I1st, Trinuclei, of the Caradoc sand- 
stone (7. Caractaci and radiatus), Asaphi, of the lower north- 
ern limestone, North American Jsotelus, in company with Swe- | 
dish Illene (I. crassicauda and centrotus); to these we must 
add, 2ndly, Calymene, of the upper Silurian formations (C. Blu- 
menbachii, C. pulchella) ; and finally, 3rdly, the Devonian genera 
Harpes, Brontes, and Arges, in beautifully distinct species. 
Besides these we find representatives of the North American 
genus Nuttainia, and splendid new species of Encrinus, Phacops, 
&c. This occurrence of Trilobites is, therefore, in a double 
point of view, the most interesting with which I am acquainted ; 
in one respect, on account of the concentration of the Trilobites 
of all formations over so small a space, and because they occur 
in a homogeneous rock. The latter circumstance favours the 
conjecture of the same external conditions of life having con- 
tinued for a long period, and readily accounts for the fact that 
Trilobites of different formations are.here united in the same 
stratum. It is hardly possible, however, that all these genera 
of Trilobites lived there at one and the same period. It is 
equally interesting on account of the association of northern 
forms, especially of Trilobites with British forms. Species com- 
mon to both the Scandinavian and English transition rock are 
rare; they are more numerous in the Irish transition rock. That 
this is the only spot in Europe where the inhabitants of the 
earliest North American oceans are found mixed with the Eu- 
ropean, may perhaps have its origin in the currents; indeed, 
even the most recent organic formations of the present day about 
Ireland would show to us a similar relation, for the ocean on the 
west coast of Ireland daily washes on shore American produce. 
The mountain limestone of Ireland, of Kildare, Cork, &c., 
which abounds in Trilobites, on the other hand exhibits the nor- 
mal character, the same succession of strata, and the same quality 
of rock as in England. It is separated from the transition rock 
by the old red sandstone, and covered by the true coal forma- 
