SCIENTIFIC SUMMARY. 
325 
as far as it has already been explored, gives an area of four miles long, by 
about eighty yards in width — this being the depth to which it is worked at 
Cwmgwynnen, in the nearly vertical strata, and at all points hitherto ex- 
amined it maintains much the same dimensions. 
The Origin of Petroleum. — The last number of the Canadian Naturalist 
contains an abstract of a recent paper by Dr. Hunt, in which the author 
alluded to the subject of the origin of petroleum. Dr. Hunt regards the 
process by which animal and vegetable hydrocarbonaceous tissues have been 
converted into solid or liquid bitumen, as a decay or fermentation, under 
conditions in which atmospheric oxygenation is excluded, so that the maxi- 
mum amount of hydrogen is retained by the carbon ; and as representing one 
extreme of a process, the other of which is found in anthracite and mineral 
charcoal, the two conditions being antagonistic, and excluding each other, 
and the production of petroleum implying, when complete, the disappearance 
of the organic tissue. Hence pyroschists, the so-called bituminous shales, 
and coal, are not found together with petroleum, but in separate formations, 
and it is to be borne in mind that the epithet bituminous applied to the former 
bodies i3 a mistaken one, since they seldom or never contain any bitumen, 
although, like all fixed organic bodies, they yield hodrocarbons by destructive 
distillation. The fallacy of the notion which ascribes petroleum to the 
action of subterranean heat on coal was exposed by Dr. Hunt, who stated 
that the oil of the Trenton limestone occurs below the horizon of any 
pyroschists or other Hydrocarbonaceous rocks. 
Dozoon Canadense. — Dr. Dawson lately presented a paper on certain 
discoveries in regard to the above fossil, before the Montreal Natural 
History Society. He also exhibited a photograph of a remarkable specimen 
of JEozoon Canadense, found during the past summer in the Laurentian 
limestone of Tudor, Canada West, by Mr. Vennor. The rocks at Tudor and 
its vicinity, which, according to the observations of Mr. Vennor, are Lower 
Laurentian, have experienced less metamorphism than is usual in formations 
of that age. And this peculiarity gives especial interest to the present 
specimen, which is contained in a rock scarcely altered, and in a condition 
not essentially different, from that of ordinary Silurian fossils. The matrix 
is a coarse laminated limestone of a dark colour, and containing much sand 
and finely comminuted carbonaceous matter. The fossil itself is of a flattened 
clavate form, about six and a half inches in length, and with the septa of its 
chambers perfectly preserved, exhibiting on one side a well-defined marginal 
wall, produced by coalescence of the septa, and apparently traversed by small 
orifices. Under the microscope the minute structures of Dozoon Canadense 
can be detected, though less distinctly perceived than in some of the speci- 
mens mineralised by serpentine. In some of the chambers there are small 
amorphous bodies containing pointed silicious spicules, which seem to be the 
remains of sponges that have established themselves in the cells after the 
animal matter of Eozoon had disappeared. 
The Classification of the Drift Deposits. — Mr. Binney writes to the 
Geological Magazine for May, to comment on Mr. Hull’s attempted classi- 
fication of the drift deposits of Lancashire and Cheshire. He states that 
25 years since he gave the following classification of these deposits to the 
Manchester Geological Society: — 1. Beds of stratified and unstratified 
