64 J. W. DAWSON ON PALZOZOIC FOSSILS 
serpentine in ophiolite, and it has a polariscope appearance approach- 
ing to that of serpentine ; while greenish by reflected light, it appears 
reddish when seen in thin slices with transmitted light. It pene- 
trates the finest pores of crinoids, and at the same time fills the cavi- 
ties of shells and the cells of corals. The larger fillings of this kind 
give the deep green spots above mentioned, while the red spots are 
apparently caused by the partial oxidation of the iron of the mineral. 
In one shell, apparently a small Orthoceras or Theca, the dark green 
filling has cracked in the manner of Septaria, and the fissures have 
been filled with carbonate of lime. In some places the mineral has 
penetrated the pores of shells of Brachiopods or crusts of Trilobites, 
producing a tubulated appearance not unlike the proper wall of 
Eozoon. 
From the characters of the fragments, I should imagine that this 
limestone is Lower Silurian rather than Cambrian. It affords an 
excellent instance of the occurrence of hydrous silicates infiltrating 
organic fragments, and it deserves the attention of collectors having 
access to the locality. A curious point of coincidence of this lime- 
stone with some of those in the Lower Silurian of Canada is the 
occurrence of a few bright green specks, probably of apatite or - 
vivianite, giving on a small scale that association of phosphates with 
hydrous silicates which we find on the great scale in the Lau- 
rentian. 
The above facts I intend to be supplementary to my papers on 
Hozoon and on the graphite and phosphates of the Laurentian already 
in England, or in such a manner as to be readily compared with each other, I 
reproduce them here :— 
Pole Hill, Llangwyllog, 
New Brunswick. Wales. 
Sill Caper Han ete saeee aaa oan ee eae 88:93 35°32 
pANITITMMIMAN Ne sacicela vitseeeweeescameececnesee 28°88 22-66 
IETROY Opa (=) Ole abROTL | SonoocascoooadoonHDGS 18:86 21:42 
IWIERATESE) sosoccosedonnacgoaqgec05000 2005006 4°25 6°98 
ZO GAISII Gili ccall bs cectec da cececeanncetecalsteeiee 1:69 1:49 
SOG aiivsse veces vaste he smawoh Wewaecseacsseeees 0-48 0:67 
Water moracrasctcceicsse eeraceuiesmitaaaclesnieeee 6°91 11:46 
| 100-00 100-00 
| 
Tu the Llangwyllog specimen the silicate amounted to three per cent. of the 
whole, the remainder being carbonate of lime with a very little siliceous sand 
and fine clay. In the Pole-Hill specimen the silicate amounted to about five 
per cent., the remainder being limestone with a few quartz grains. 
It will be seen that these two silicates, evidently deposited from solution in 
such a manner as to fill the finest organic pores, are remarkably similar in com- 
position ; and the fact that they closely resemble Hotfmann’s mineral found in 
Bohemian Hozoon, and also the loganite filling the Burgess Hozoon (Quart. Journ. 
Geol. Soc. vol. xxi. 1865), gives them additional interest. 
