462 ORIGIN OF ERUPTIVE AND PRIMARY ROCKS. 



similar to those so well described by Nauru ana in referring to the 

 parallel structure of certain igneous rocks ?•* There are not want- 

 ing instances of the formation of a slaty structure in artificially 

 formed slags, from a similar cause. Nothing is more common 

 than to observe in slags from iron-furnaces a distinct streaked ox 

 banded appearance, evidently caused by the different rate of 

 motion in the interior and outside parts of the flowing stream of 

 slag. This phenomenon I have often observed at the Eglinton 

 iron-works, Scotland, and more recently at Bethlehem, Pennsyl- 

 vania. It is simply another instance of the production of a strati- 

 -fied appearance, similar to those described by Tyndall in his work 

 •«* On the Glaciers of the Alps." In this work he shows that the 

 banded appearance of glacier-ice, the lamination of wax subjected 

 to pressure, and the fibrous texture of rolled iron, are caused by 

 the motion under pressure of the atoms constituting those sub- 

 stances. Not only has a banded structure been observed among 

 certain furnace scoriae, but the latter have even been observed to 

 possess sometimes both fibrous and foliated structures. The raw 

 slag from the " Frischfeuer " at Bieber in Hessia, possesses a 

 marked fibrous texture, and slag with a distinct slaty texture is 

 produced at the blast-furnace in M&gdesprung. The latter is 

 formed swimming on melted iron, while its surface comes in con- 

 tact with the cold air. Small pieces ot this slag resemble the re- 

 fuse of roofing slate, not only in their appearance, but also in 

 their cleavage. In larger pieces perfectly vitreous layers are com- 

 bined with the slaty ones, both graduating into each other .f 

 From these instances, and considering that the existence of inter- 

 nal currents at t k it period is highly probable, it would appear 

 not unreasonable to expect that some of the rocks solidified on 

 the surface of the fluid globe, would have a schistose structure. It is 

 impossible to suppose that the particles of the fluid material be- 

 neath the solidifying crust, would always preserve the same rela- 

 tive position to the latter, in spite of the daily revolution of the 

 globe. The liquid rock beneath the crust must have moved in 

 one direction or other almost as freely as the water of a frozen 

 river under the ice which covers it. The schistose structure re- 

 sulting from this solidification under motion must however have 

 resembled more the foliation of certain igneous rocks than the 



* Canadian Naturalist, vol. viii. p. 375. _ 



fVon Leonhard, Hiittenerzeugnisse und andere auf kunstlichem wege 

 gebildete Mineralien als Stutzpunkte geologischer Hypothesen, p. 156. 



