54 J. W. DAWSON ON THE MICROSCOPIC 
in imperfectly preserved specimens. I have not been able to satisfy 
myself whether these lines of growth are of specific value. In one 
specimen from the Devonian of Lowa, a Stromatopora of this type 
presents large vertical tubes which extend from one growth-line to 
the next, but are sparsely distributed through the mass, and not 
connected with radiating tubes as in Caunopora. 
Another interesting structure, seen in a species from the Cornife- 
rous Limestone, usually, though perhaps incorrectly, identified with 
S. concentrica, 1s the division of the pillars at their summits into 
branches (PI. III. fig. 2), so as to support at many points the layer 
above, which in this case is thin and not much strengthened with 
supplemental deposit. 
2nd. State of Preservation.—Stromatopore have apparently always 
been calcareous when recent. They are sometimes preserved in the 
state of calcite with the chambers either filled with the same mate- 
rial or with silica. Sometimes they are entirely silicified, or the 
lamine and pillars are silicified and the chambers filled with calcite. 
Occasionally the chambers are filled with dolomite or the whole 
structure is dolomitized. 
A specimen of the type of S. concentrica from the Devonian or 
Upper Silurian of James’s Bay is now before me, and affords a good 
illustration of modes of preservation in silica. In some places the 
lamin and pillars haye been silicified, while the chambers are filled 
with limestone. When weathered or treated with acid, these portions 
show the whole structure very clearly, including the perforations of 
the laminee and the hollow pillars (PI. IV. fig.7). Other portions have 
the chambers also filled with silica, the laminee being distinguishable 
by their less transparent and porous character. In these portions the 
lamin and pillars have usually been first coated over with minute 
erystals of quartz. A layer has then been deposited of chalcedony 
with botryoidal surfaces, and finally the remaining cavities have been 
filled with crystalline vitreous quartz. In the greater part of the 
specimen, however, the chambers have been filled with silica, while 
the laminee have remained as calcite, and these portions, when 
weathered, present the appearance of thick structureless lamin 
separated by thin spaces and penetrated by numerous round holes 
representing the pillars. Portions in this state might be mistaken 
for a coral of the type of /Mstulipora, but im certain aspects they 
present that lobated amoeboid form which is so characteristic of 
similarly preserved specimens of Hozoon. 
In specimens of Stromatopora from the Niagara Limestone, it 
not unfrequently happens that certain layers or groups of layers 
are silicified, while others alternating with them remain as calcite. 
In this case, when the specimens are weathered, they present distant 
concentric layers very different in appearance’ from the actual 
structure. 
As with other fossils, crystallization plays strange freaks with 
Stromatopore, reducing them to such a condition that, but for the 
partial preservation of portions here and there, they might be mis- 
taken for inorganic hodies, This is well seen in the abundant Stro- 
