R. DOW ON AN OUTCROP OF DIABASE AT ROSSIE PRIORY. 
5 
daily observation that Nature hastens to cover over and heal up the 
scars inflicted by the operations of man on her fair face; the same 
law is applicable to the scars and rents inflicted by the giant hand 
of Nature on herself. 
The decomposition product found so abundantly in the Knapp 
Quarry consists of a variety of serpentine, a silicate of magnesia 
derived from the disintegration of the augite, but principally from the 
olivine present in the basalt. This product is quite soft, and may 
easily be scratched by the finger nails. It produces a white powder 
which does not effervesce with acids; on fresh specimens the rock 
has a peculiar polished surface. It has the same unctuous or oily 
touch as steatite when rubbed by the hand. The lustrous surface 
slowly tarnishes on exposure to the air. Talc, soapstone, and meer- 
chaum have a somewhat similar composition, with a difference in the 
quantity of the various mineral constituents. 
When so much internal decomposition has been going on ever 
since the rock appeared, it must differ considerably from such basalts 
as we find in the trap dykes where little or no alteration has taken 
place. To differentiate a basalt such as has been described when the 
silicates, especially augite and olivine, have undergone a long decom¬ 
posing process, the name diabase has been applied. As popularly 
known, a basalt and dolerite have the same constituents. In the 
case of a basalt the component minerals are too fine grained to be 
separately determined except by the aid of a microscope ; a dolerite 
is a coarser basalt, in which the minerals can be recognised with the 
naked eye; a diabase is an altered dolerite. Many of our lavas of 
early geological times are to a large extent diabase. The greenish 
serpentine coating sometimes assumes a fibrous structure, forming 
the mineral picrolite, a fibrous variety of serpentine. 
A few veins of calcite fall to be noticed. These are of abnormal 
thickness in some cases, and of great persistence in the rock mass. 
In one part of the quarry a series of perpendicular calcite veins 
extend from the top to the base of the exposed rock. The calcite is 
removed in solution by permeating water ; it may either be a foreign 
product brought from above or at a distance, or it may be the result of 
decomposition in the rock itself. In some of the veins the two pre¬ 
cipitations of calcite and magnesia are seen to have gone on contem¬ 
poraneously ; in others the chlorite has failed to entirely fill up the 
vein, but the deposition of calcium carbonate has followed and 
has completely filled up the entire cavity. 
At the base of the quarry the rock consists of a very coarse¬ 
grained dolerite, with a macro-crystalline structure ; the large elon¬ 
gated pinkish crystals are plagioclase felspar. On fresh unweathered 
faces the crystals appear as glassy strips or rods, on which may be 
