100 Murchison— Laurentian Rocks. 
interest; and, combined with the geological sections of those 
mountains which I published in ‘ Siluria’ (p. 100), assures 
us that, in the North-west of Ireland, as in the North-west of 
Scotland, we have a true Lower Laurentian rock. Indeed 
the mineral characters of the Irish and Canadian rocks are also 
assimilated by containing much serpentine. 
It is also of high geological importance to observe, that the 
strike of this Irish limestone with Kozoon is like that which I 
described in Scotland, namely, from South-east to North-west.. 
In a communication to the French Academy of Sciences some 
years ago, I specially called attention to this striking fact—that 
the direction of the Laurentian gneiss of Scotland was at right 
angles to that of all the superjacent rocks of Britain, throughout 
which country the Cambrian and Silurian rocks everywhere 
trend from NE. to SW. 
Finally, as to the Laurentian rocks of Bavaria and Bohemia, 
which are not noticed im the ‘ Elements.’ In the year 1862 I 
satisfied myself by personal researches* that the ‘ Primordial’ 
Silurian zone of Barrande was, in Bavaria and the adjacent 
parts of Bohemia, underlain (as shown by Giimbel) by a very 
vast thickness of clay-slate, which, though not so much altered 
as the overlying strata containing fossils, had as yet afforded no 
traces of them. It was underneath these vast masses, united 
with subjacent metamorphosed crystalline schists, also of great 
thickness, and considered, as a whole, to represent the Cambrian 
rocks, that the grand mountains of an older gneiss rise up. I 
had no hesitation, therefore, in referring this ancient gneiss in 
the heart of Germany, and of which there is a younger and an 
older mass, to the Laurentian age, as well as the fundamental 
rocks of Britain above spoken of. If English writers have 
failed to allude to this great feature in the geological structure 
of Germany, as proved by order of infraposition (a natural 
result, indeed, of the previous labours of Barrande and Giimbel), 
there are authors in Germany who have not failed to record 
the importance of the conclusion at which I arrived, and which 
I thus expressed :— 
‘If all the true gneissic rocks of Bavaria (and Bohemia) be 
united, they may well, from their colossal dimensions, stand in 
the place of the Laurentian Gneiss of Canada and of the North- 
west of Scotland. The clear evidence which exists of the in- 
terpolation of a vast thickness of sedimentary formations, in 
which no fossils have been found, between the great gneissose 
* Quart. Journ. Geol. Soc., vol. xix. p. 854, &e. 
