170 Professor Keilhau on Unstratified 



like other fossiliferous rocks, was originally sedimentary. 

 The examples given by Murchison (Silurian System, vol. i. 

 chapters 19, 21, &c.) of the occurrence of petrifactions 

 in different traps or similar rocks, are among the newest facts 

 of this kind ; and they can so much the less be rejected 

 by geologists of the present day, because the author, as is 

 well known, is a zealous volcanist. His having in this 

 capacity arbitrarily assigned peculiar names to these rocks 

 containing fossils, cannot much stand in the way of our pro- 

 per apprehension of their real nature, and only shews how 

 little the system, which it is so constantly the endeavour to 

 support, is applicable to the very phenomena which are so 

 distinctly and fully opened up to view. Murchison recog- 

 nised perfectly distinct traces of encrinites, trilobites, and 

 other Silurian organisms, in masses which, according to the 

 petrographical description given, must be sometimes perfect- 

 ly characteristic syenite, sometimes greenstone, sometimes 

 a kind of felspar porphyry, &;c. As these masses, according 

 to the statement of the author, frequently pass into the stra- 

 tified and mechanically deposited rocks in which, as their 

 original repositories, fossils generally occur, there is no 

 reason for supposing that the organic remains met with in 

 these crystalline rocks, proceed from petrifactions derived 

 from any other quarter. Murchison has also really acknow- 

 ledged that these animal remains existed from the first in the 

 masses which he found presenting the characters of the above 

 mentioned crystalline silicide rocks. Lastly, it is also wor- 

 thy of all attention, that he describes these masses as hav- 

 ing, for the most part, the nature of beds, and frequently 

 alternating, in this form, with sandstone, slates, <&c., but, ne- 

 vertheless, sometimes constituting one mass with the amor- 

 phous portions of the same rock which frequently occur at the 

 same localities. Murchison's descriptions are in the highest 

 degree convincing : it is perfectly evident that, at particu- 

 lar places, many of the silurian strata have been either par- 

 tially or entirely converted into trap or other similar rocks. 

 Even the volcanic language employed on the same occasion 

 must contribute to strengthen this conviction ; for it sounds 

 quite like irony, and the explanation offered is really a cari- 



