Page:Popular Science Monthly Volume 10.djvu/284

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dawn-animal. Logan speaks of it in his first remarks upon them, referring more particularly to their weathered outcrops and somewhat concentric structure; while Dawson sees much in their internal organization suggestive of a fitness for foraminiferal requirement. The layer seems better arranged for sheltering a gelatinous body, throwing out pseudopodia reaching after food, than for accommodating the

PSM V10 D284 Stromatopora concentrica.jpg
Fig. 9.—Stromatopora Concentrica. (Goldf.)
1. Surface of a small hemispheric mass, showing the edges of the thin laminae unequally weathered, natural size.
2. Magnified portion, showing weathered edges of successive lamina?, which are indented by pores.
3. More highly-magnified portion of the specimen, showing the walls and tubulation.

sponge animals, subsisting through the passage of currents of water. The canal system, with the supplemental skeleton, is wanting in this genus, but appears in the allied forms of the Devonian.

A very important feature of the greenstone fossils is their mineral composition. They are composed of silicates, very probably of feldspar. Mr. Hawes has not been able yet to satisfy himself fully as to the nature of the silicate, because of the smallness of the particles obtained. A drop of acid placed upon one of the specimens exhibited a slight effervescence, indicating the traces of carbonate of lime—perhaps part of the original foraminifer before its fracture and dispersion in the mud. He suggests that the presence of these lime-structures afforded the material for the manufacture of so much labradorite in the diabases containing the fossils.