98 
IDDINGS. 
Bunsen’s theory was not long permitted to go unassailed. 
Two years later, in 1853, Sartorius yon Waltershausen pub¬ 
lished the results of his studies of the volcanic rocks of Etna 
and Iceland.* In this work he combined the chemical study 
of the essential minerals of rocks with certain physical con¬ 
ditions of the earth, and what were then considered by 
some to be well-established geological facts. The chemical 
portion of the theory was grounded very largely on the grada¬ 
tion in composition and specific gravity of the feldspar series, 
which was made to include a species called krablite, with 
from 74 to 80 per cent, of silica; so that albite and orthoclase 
occurred in the middle of the series instead of at the most 
silicious end, as at present, since krablite has been found to 
be a rock. A consideration of the mean specific gravity of 
the earth and that of the elements forming its crust with¬ 
out allowing for a possible influence of pressure on the ma¬ 
terial within the globe led him to conceive of the earth as 
being made up of concentric shells of variable specific gravity, 
increasing from that of quartz at the surface to that of bis¬ 
muth and silver at the center. It was also thought to have 
been established that the earliest igneous rocks which had 
been, erupted in past geological ages were highly feldspathic 
and silicious ones, allied to granites, and that more recent 
ones were less silicious, and the most recent lavas the most 
basic; and the gradual cooling of the globe having consoli¬ 
dated the molten interior at gradually increasing depths, 
the earlier eruptions would have come from nearer the sur¬ 
face than the later ones. 
These considerations led Von Waltershausen to the theory 
that “ the whole exterior crust of the earth is to be considered 
as having been originally a feldspar mass, which contained 
at the surface relatively very few foreign mineral bodies, but 
which came to an end at a depth of about 94J miles, after it 
had reached its most basic composition, and was followed by 
specifically heavier silicates and metal oxides, especially by 
*Von Waltershausen (S.) Uber die vulkanischen Gesteine inSicilien 
und Island, etc. 8°. Gottingen, 1853. 
