PROGRESS OF MICROSCOPICAL SCIENCE. 
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internal structures, corresponding to wliat might have been expected 
on the hypothesis of its organic origin, are added to it ? If I affirm 
that a certain mass is the trunk of a fossil tree, and another asserts 
that it is a concretion, but professes to be unable to account for its 
form and its rings of growth, surely his case becomes very weak after 
I have made a slice of it, and have shown that it retains the structure 
of wood. Next, they appear to admit that if sjDecimens occur wholly 
composed of carbonate of lime their theory will foil to the ground. 
Now such specimens do exist. They treat the Tudor specimen with 
scepticism as probably * strings of segregated calcite.’ Since the 
account of that specimen was published, additional fragments have 
been collected, so that new slices have been prepared. I have ex- 
amined these with care, and am prepared to affirm that the chambers 
in these specimens are filled with a dark-coloured limestone not more 
crystalline than is usual in the Silurian rocks, and that the chamber 
walls are composed of carbonate of lime, with the canals filled with 
same material, except where the limestone filling the chambers has 
penetrated into parts of the larger ones. I should add that the 
strati grajffiical researches of Mr. Vennor, of the Canadian Survey, 
have rendered it probable that the beds containing these fossils, though 
unconformably underlying the Lower Silurian, overlie the Lower 
Laurentian of the locality, and are, therefore, probably Upper Lau- 
rentian, or perhaps Huronian, so that the Tudor specimens may 
approach in age to Giimbel’s Euzoon Bavaicum. Further, the authors 
of the paper have no right to object to our regarding the laminated 
specimens as ‘ typical ’ Eozoon. If the question were as to typical 
ophite, the case would be different ; but the question actually is as to 
certain well-defined forms which we regard as fossils, and allege to 
have organic structure on the small scale, as well as lamination on 
the large scale. We profess to account for the acervuline forms by 
the irregular growth at the surface of the organisms, and by the 
breaking of them into fragments confusedly intermingled in great 
thickness of limestone, just as fragments of corals occur in Palaeozoic 
limestone ; but we are under no obligation to accept irregular or 
disintegrated specimens as typical, and when objectors reason from 
these fragments we have a right to point to the more perfect examples. 
It would be easy to explain the loose cells of Tetradium, which 
characterize the Bird’s-eye limestone of the Lower Silurian of America, 
as crystalline structures ; but a comparison with the unbroken masses 
of the same coral shows their true nature. I have for some time 
made the minute structure of Palfeozoic limestones a special study, 
and have described some of them in the Trenton formation of Canada. 
I propose shortly to publish additional examples showing fragments 
of various kinds of fossils preserved in these limestones, and recog- 
nizable only by the infiltration of their pores and other minute 
structures. I shall also be able to show that in many cases the 
crystallization of the carbonate of lime and the infiltration of other 
substances have not interfered with the perfection of the most minute 
of these structures. The fact that the chambers are usually filled 
with silicates is strangely regarded by the authors as an argument 
