ON AN EXPERIMENTAL INVESTIGATION INTO THE FLOW OF MARBLE. 397 
19. Limestone. Farniaen , Switzerland. —Near the eastern end of the Susten Pass 
a synclinal of Mesozoic rocks is pinched in by the folding of the Alps. Among these 
at Farnigen is a very fine-grained, slabby, blue limestone, which is of especial interest 
in that it contains numerous belemnites, which have been greatly elongated and in 
some cases torn apart. The rock shows no signs of recrystallisation, except that 
white calcite has been deposited between the fragments of the broken belemnites. 
Under the microscope it is seen to be composed of very minute elongated calcite 
grains, like those above described. There are also dotted all through the rock, groups 
of darker coloured grains of a rhombohedral carbonate, probably dolomite. These are 
untwinned and apparently uncrushed. The foliation of the rock, due to the flattening 
of the calcite grains, curves around them as it does around the garnets in a schist. 
There are also lines of more coarsely crystalline calcite, as described in No. 5, whose 
origin is identical in both cases. 
20. Limestone. Meienthal, Switzerland. —Other specimens in the Zurich collection 
labelled simply “ Meienthal,” but probably also from near Farnigen, show exactly the 
same structure as described in No. 19. The little elongated calcite grains not having 
an identical orientation extinguish between crossed Nicols in different positions. 
21. Limestone. Haslithal, Switzerland. —This rock, which is a typical example of 
Heim’s 4 Bruchlose gefaltete Malm Kalk,’ shows the same flattening of the minute 
calcite individuals composing it. The little calcite veins referred to in No. 5 are here 
folded in with the rock and are more coarsely crystalline. Their presence shows that 
the rock was at first brittle and became shattered under the pressure, the fissures 
thus formed becoming filled and giving rise to calcite veins more coarsely crystalline 
in character than the rest of the rock. With the continuance of the pressure the 
rock became plastic and the veins were folded, the calcite grains composing them 
becoming flattened like those constituting the mass of the rock. The plane of the 
flattening or foliation of the grains cuts across the veins quite irrespective of their 
course, the position of the latter being marked by their lighter colour and coarser 
grain. The motion evidently took place in connection with the flattening of the 
calcite grains, and possibly, as above noted, by their movements over each other. 
Limestones and Marbles not showing any Distinct Pressure Structures. 
The limestones and marbles of this class (Nos. 22 to 42) do not here merit indi¬ 
vidual description. They do not present any undoubted evidence of movement under 
pressure. Their structure is that of a mosaic, apparently resulting in each case from 
the recrystallisation of a previously existing finer-grained limestone. This process, as 
described by Lepsius # in the Attic marbles, consists of the enlargement or growth of 
certain of the constituent grains at the expense of others until finally a coarse-grained 
mosaic is produced. Traces of this are seen in several of these rocks. Twinning is 
* ‘Geologie von Attika; ein Beitrag zur Lehre vom Metamorphismus der Gesteine,’ p. 186. 
