MINERALIZED WITH SILICATES. 65 
published in the Journal of this Society, and as illustrative more 
especially of the affinity of Hozoon with its successors in function, 
the Silurian Stromatopore, and of the abundant occurrence of ser- 
pentine and other hydrous silicates in association with fossils in the 
Lower Silurian as well as in the older Laurentian. 
ILI. Iwirative Forms resemBiine Eozoon. 
It is easy for inexperienced observers to mistake laminated con- 
cretions and laminated rocks either for Stromatopora or for Hozoon, 
and such misapprehensions are not of unfrequent occurrence. As to 
concretions, it is only necessary to say that these, when they show 
concentric layers, ave deficient altogether in the primary require- 
ments of laming and interspaces ; and under the microscope their 
structures are either merely fragmental, as in ordinary argillaceous 
and calcareous concretions, or they have radiating crystalline fibres 
like oolitic grains. Laminated rocks, on the other hand, present 
alternate layers of different mineral substances, but are destitute of 
minute structures, and are either parallel to the bedding or to the 
planes of dykes and igneous masses. In the Montreal mountain 
there are beautiful examples of a banded dolerite in alternate layers 
of black pyroxene and white felspar. These occur at the junction 
of the dolerite with the Silurian limestone through which it has been 
erupted. Laminated gneissose beds also abound in the Laurentian. 
Still more remarkable examples are afforded by altered rocks having 
thin calcite bands, whether arising from deposition or from vein- 
segregation. One of these now before me is a specimen from the 
collection of Dr. Newberry, and obtained at Gouverneur, St. Law- 
rence County, New York. It presents thick bands of a peculiar 
granitoid rock containing highly crystalline felspar and mica with 
grains of serpentine; these bands are almost a quarter of an inch 
in thickness, and are separated by interrupted parallel bands of 
ealcite much thinner than the others. The whole resembles a mag- 
nified specimen of Hozoon, except in the absence of the connecting 
chamber-walls and of the characteristic structures. A similar rock 
has been obtained by Mr. Vennor on the Gatineau; but it is less 
coarse in texture though equally crystalline, and appears to contain 
hornblende and pyroxene. ‘These are both Laurentian, and I con- 
sider it not impossible that they may have been organic; but they 
lack the evidence of minute structure, and differ in important details 
from Hozoon. Another specimen from the Horseshoe Mountain in 
the Western States (I regret that I have mislaid the name of the 
gentleman to whom I am indebted for this specimen) is a limestone 
with perfectly regular and uniform layers of minute rhombohedral 
crystals of dolomite. ‘The layers vary in distance regularly in the 
thickness of the specimen from two millimetres to one, and must 
have resulted from the alternate deposition in a very regular manner 
of dolomite and limestone. ‘These are but a few of the examples of 
imitative structures which might readily be confounded with Kozoon, 
or which, if resulting from organic growth, have lost all decisive 
evidence of the fact. 
Perhaps still more puzzling imitative forms are those referred to 
Q.J.G.8. No. 137. F 
