Penny Blood: Serial Sensation and Working-Class Entertainment — page 274: what you’re looking at

Machine-transcribed from the original scan — historical spelling and the odd misread are preserved.

cu. xx.) SEQUENCE OF VOLCANIC ROCKS. 257 of eruption the heavier and lighter elements of the contents of these subterraneous reservoirs appear mingled together; but in the later stages of the volcanic history of the district, the lighter or acid elements rise to the top and the heavier or basic sink to the bottom, and we have separate eruptions of rhyolite and basalt.” But he gives no reason for this original mixture of the magmas and for their subsequent separation. According to our view, however, the succession of Richthofen seems to be the necessary one. Before the rending of the fissures occurred, which we suppose to have elevated the moun- tain chain, the different magmas occupied the positions and sequence determined by their densities, and consequently the acid magma being already solidified in the crust, the first erupted of the rocks would be intermediate in respect of their specific gravity, and acidity. But this very injective action itself would depress the acid crust in a protuberant ridge, presenting to the denser substratum an under surface, which would be but just below the temperature of its fusion. This surface now becoming fused, would underflow the crust, and the next time that an eruption took place in that region, a more acid and lighter lava would make its appearance. But at other places, out of the reach of the flow of this acid remelted matter, or at the same place after the layer of it thus formed had been ejected, the subjacent basic magma would furnish the lava next in sequence. The same hypothesis appears capable of accounting for such a circumstance, as that mentioned by Prof. Judd regarding the adjacent volcanic districts of Hungary and Bohemia‘. The pro- ducts of the contemporaneous later tertiary outbursts in these adjacent areas were “as different in character as can well be imagined,” so that “it is scarcely possible to imagine that such very different classes of lavas could have been poured out from vents which were in communication with the same reservoirs of igneous rock, and we are driven to conclude that the Hungarian and Bohemian volcanoes were supplied from different sources.” According to our view they were so; because the areas which 1 Ibid. p. 202. F. 17 COLA @ NOO (CO)