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PROFESSOR F. D. ADAMS AND DR. J. T. NICOLSOX 
one another and thus always adapting their shape to the space to he occupied, or 
whether the structure is in part due to recrystallisation, is not perfectly certain. Heim 
holds the former view, and believes that microclivage and fluidal structure are essen¬ 
tially the same. “ Es gibt in der That,” he writes, “ keine Grenze und keinen wirklichen 
mechanischen Unterschied zwischen beiden.”* If this be the true explanation of the 
structure, these rocks are closely related to those of the class just described. We 
intend in a subsequent series of experiments, making use of fine-grained limestones, to 
endeavour to reproduce this structure also by artificial compression, and thus, it 
possible, to determine its origin. 
16. Limestone. Langis Grat, Switzerland .—A fine-grained grey limestone from the 
Langis Grat, which rises above the Furka Road, opposite the Rhone Glacier, and 
which is believed to be a continuation of the same limestone as that which further 
east appears as the Andermatt marble (No. 3). It breaks up into long thin chip-like 
fragments, and where it disintegrates in damp places falls into a mass of needle-like 
calcite grains. It is indistinctly streaked in very narrow lines in lighter and darker 
shades. With the exception of a little carbonaceous matter and a few mica plates it 
consists altogether of calcite. In some places it holds belemnites. It has a very 
distinct foliated structure, due to the calcite grains being all flattened in one direction. 
The mass of the rock is made up of very small grains, but there are at intervals lines 
of similarly flattened grains of larger size. As shown by the study of longitudinal 
and transverse sections, the grains have the shape of short laths of irregular outline, 
resembling very closely in form the little leaves of quartz seen in certain gneisses, and 
are frequently as much as six times as long as they are wide. The larger grains are 
frequently twinned, hut the smaller grains rarely show this structure. Strain 
shadows are not seen. It seems doubtful whether this structure is attributable to 
recrystallisation in the case of such a fine-grained limestone which still retains its 
organic pigment. It is not cataclastic, but may be due to the flattening of the calcite 
grains by gliding, under the influence of the great pressure to which the rock has 
been subjected. 
17. Limestone. L,ochseite, Switzerland. —The Malm limestone which is such a 
striking element in the succession in the Glarner Double Fold, and which derives its 
local name from Lochseite, near Schwanden, presents the same flattening of the 
constituent calcite grains as described in No. 16. The rock from Lochseite itself is 
very impure and extremely fine in grain, so that the structure is not well seen, but 
the elongation or flattening of the minute calcite grains composing the rock was 
observed in a number of slides of the Lochseiten-Kalk from various localities, which 
are preserved in the collections of the Geological Department of the University of 
Zurich. 
18. Limestone. Saasberg, Switzerland. —The rock from the Saasberg, near the 
Butzistdekli, shows this structure excellentlv. 
* ‘ Untersuchungen iiber den Meehanismus dor Gebirgsbildung,’ Bd. 2, p. 56. 
