60. J. W. DAWSON ON PALZOZOIC FOSSILS 
or shales, with thin bands of limestone holding fragments of Lower 
Silurian corals and crinoids. These pass upwards into a thick series 
of slaty rocks characterized by the prevalence of a shining crystal- 
line hydro-mica, and known as nacreous or hydro-mica slates. They 
are associated with quartzose bands, and also with lenticular layers 
of crinoidal limestone. Parallel with these beds and, according to 
Logan’s observations, overlying them, is the series containing the 
serpentine, which is associated with layers of limestone and nacre- 
ous slate, and also with brecciated and arenaceous beds, probably 
originally tufaceous, with beds of anorthite, steatite, and dolomite, 
and also with red slates, the whole forming a miscellaneous and ir- 
regular group, evidently resulting from the contemporaneous action 
of igneous and aqueous agencies, and affording few traces of fossils. 
The serpentines, which occur in thick and irregular beds, are differ- 
ent in colour and microscopic texture from those of the Laurentian 
system, and also present some chemical differences, more especially 
in the presence of oxides of nickel, chromium, and cobalt, and of a 
larger percentage of iron and a smaller proportion of water*. 
These serpentines are undoubtedly bedded rocks and not eruptive ; 
but they may have originated from the alteration of voicanic mate- 
rialst. They appear, shortly after their original deposition, to have 
been broken up, so as in many places to present a brecciated ap- 
pearance, the interstices of the fragments being filled with limestone 
and dolomite, which themselves are largely mixed with the flocculent 
serpentinous matter, and traversed by serpentinous veins some- 
times compact and sometimes fibrous. Besides the very impure 
limestone thus occurring in the serpentinous breccia, there are also 
true layers or beds of limestone and dolomite included in or near to 
the great serpentine band. No well-preserved fossils have been 
found either in these beds or in the brecciated serpentine; but on 
treating the surfaces of slabs with an acid or making thin slices, 
fragments of organic bodies are developed which well illustrate the 
manner in which serpentine, whatever its origin, may be connected 
with the mineralization of such fragments. 
It is to be observed here that the irregular bedding of the serpen- 
tine, and the apparent passage on the line of strike into dolomite 
and red slate, might accord either with a purely aqueous and oceanic 
mode of deposition like that of glauconite, or with deposition as beds 
of volcanic sediments, afterwards altered and partly redeposited by 
water. The association with ash rocks and agglomerates would, how- 
* Under the microscope the Laurentian serpentines are usually homogeneous 
and uncrystalline, but with the structure of netting veinlets which I have 
elsewhere called septariform. The Melbourne serpentines usually present a 
confused mass of acicular crystals or a fibrous structure, and, where structure- 
less, polarize more vividly than those of the Laurentian. 
t Sandberger (Essay on Metallic Veins) quotes many German chemists to 
the effect that “olivine rock and the serpentine formed from it always contain 
copper, nickel, and cobalt.” This origin might thus apply to the serpentines in 
the Quebec group in Canada, but not to those of the Laurentian, as I have 
already urged on other grounds in my reply to Hahn, in the ‘Annals and 
Magazine of Natural History,’ 1876, vol. xviii. pp. 32, 33, 
