ON AN EXPERIMENTAL INVESTIGATION INTO THE FLOW OF MARBLE. 393 
Griesbach limestone cannot be distinguished under the microscope from the Carrara 
marble deformed at 400° C., the structures being identical. A microphotograph of 
this rock is shown on Plate 22, fig. 3. It was taken between crossed Nicols in 
polarised light and is magnified 70 diameters. The rock also contains a few grains 
of quartz and muscovite which usually show marked strain shadows. 
8. Marble. Carrara, Italy .—Carrara marble is usually free from any evidence of 
pressure or deformation, its normal character being that of the marble described and 
figured in the former part of this paper, and upon which the experiments in deforma¬ 
tion were carried out. In this specimen, however, there is a suggestion of parallelism 
in the glistening cleavage surfaces of the broken rock, and under the microscope the 
calcite grains show a distinct tendency to assume a flattened form. A very large 
proportion of the grains are twinned, and strain shadows are seen in some cases. The 
appearance of the sections indicates that the flattening of the grains has been 
produced by movements along gliding planes under the influence of dynamic actiou. 
As in the case of No. 15, pressure acting subsequent to the recrystallisation of the 
rock has probably set up movements in certain parts of the mass, from one of which 
this specimen has been derived. 
Nos. 9 to 15 are from the Grenville series, of the Laurentian system, of Canada. 
The first six are from the counties of Peterborough and Hastings, in the province of 
Ontario, in the district to the north of the lake ot that name, and the last is from a 
point about 40 miles west of Montreal, in the province of Quebec. 
9. Marble. Lot 12, Range V., Township of Burleigh, Ontario. —This marble comes 
from the same great limestone belt as Nos. 10 and 11, although several miles distant 
from the locality from which the latter was obtained. The stratigraphical relations 
point to great movements along this line, a fact which is borne out by the structure 
of the limestones themselves. The limestone at this locality is coarsely crystalline, in 
some cases becoming very coarse, the constituent grains being as much as an inch in 
diameter. As in the case of the Carrara deposits, it is for the most part massive and 
free from any foliation, but along certain lines or bands it presents a very marked 
foliation, and cataclastic structure is distinctly seen in hand specimens, large and 
more or less lenticular and much twisted calcite remnants lying with their longer axes 
parallel to one another in a fine-grained base derived from their partial destruction. 
Under the microscope the evidence of this action is most striking. The large remnants 
are twinned and curved, showing marked strain shadows, and can in many cases be 
seen to be in the act of breaking down into smaller grains, especially about their 
margins. A microphotograph of the rock is shown in Plate 25, fig. 3. It is taken 
between crossed Nicols in polarised light, and is magnified 47 diameters. In the 
small grains constituting the base twinning and strain shadows are also frequently 
seen, and there is presented a distinct tendency to flattening in the same direction 
as that in which the longer axes of the large remnants lie. A number of twisted 
grains of quartz, showing very marked strain shadows, and in some cases even a 
marked granulation, are also present in the rock. 
yol. cxcv.— a. 3 E 
