H. COATES AND P. MACNAIR ON BANDED HORNBLENDE SCHIST. l6l 
shire. At Balhoulan Quarry, in contact and along the sill, bands of 
limestone appear, and we have also detected bands of calcite in the 
hornblende schists occurring in a similar manner to the bands of grit 
and conglomerate just described. What the reason of this constant 
association of these two rocks may be we cannot say, nor do we 
believe that the data at Balhoulan Quarry are sufficient to determine 
it. Sir Archibald Geikie also notices this fact in his Presidential 
Address to the Geological Society of London for the year 1891.* 
Numerous foldings of the rock are to be seen in the quarry. One 
very large and striking example is over two feet in depth, the lines of 
schistosity being bent back upon each other to that extent (see Plate 
II.). It seems to us that the occurrence of these folds indicates that 
the process of shearing and metamorphism must have been the con¬ 
sequence of a series of intermittent forces rather than of a continuous 
Fig. II. Microscopic Section of Banded Hornblende Schist from Balhoulan Quarry. 
X 50 Diameters. 
Strain, for it is difficult to conceive how the puckering and banding 
could both have been produced at the same time, as the banding or 
drawing out of the included fragmental portions of the sill must first 
have taken place, and the plication of these bands into folds been the 
result of a second application of the shearing and straining forces. 
In Fig. II. we have given a drawing of the banded horn¬ 
blende schist as seen under the microscope. The section has been 
cut at right angles to the plane of schistosity. The rock consists 
essentially of long prism-shaped crystals and grains of hornblende, 
thickly scattered through a ground mass of felspar and quartz. The 
latter minerals also occur in the granular form so common amongst 
these altered basic rocks, and which so closely simulates the frag- 
* Qnar. Jour, Geol. Soc., Vol. XLVIL, p. 76. 
