THE LAURENTIAN AND HURONIAN PERIODS. 69 
penter and Dawson, from the standpoint that it is a genuine 
organism—the balance of evidence up to this moment inclin- 
ing decisively to this view. 
The structure known as £ozoon is found in various localities 
in the Lower Laurentian limestones of Canada, in the form of 
isolated masses or spreading layers, which are composed of 
thin alternating laminz, arranged more or less concentrically 
(fig. 22). The laminz of these masses are usually of different 
Fig. 22.—Fragment of Eozoén, of the natural size, showing alternate lamine 
of loganite and dolomite. (After Dawson.) 
colours and composition ; one series being white, and com- 
posed of carbonate of lime—whilst the lamine of the second 
series alternate with the preceding, are green in colour, and 
are found by chemical analysis to consist of some silicate, 
generally serpentine or the closely-related “‘loganite.” In 
some instances, however, all the laminz are calcareous, the 
concentric arrangement still remaining visible in consequence 
of the fact that the Jaminz are composed alternately of lighter 
and darker coloured limestone. 
When first discovered, the masses of Lozodn were supposed 
to be of a mineral nature; but their striking general resem- 
blance to the undoubted fossils which will be subsequently 
spoken of under the name of Stromatopora was recognised by 
Sir William Logan, and specimens were submitted for minute 
examination, first to Principal Dawson, and subsequently to 
Die WizB. Carpenter. After a careful microscopic examina- 
tion, these two distinguished observers came to the conclusion 
that Lozodn was truly organic, and in this opinion they were 
afterwards corroborated by other high authorities (Mr W. K. 
Parker, Profesor Rupert Jones, Mr H. B. Brady, Professor 
Giimbel, &c.) Stated briefly, the structure of Hozodn, as ex- 
hibited by the microscope, is as follows :— 
