23a 
PROCEEDINGS OF THE PERTHSHIRE SOCIETY OF NATURAL SCIENCE, 
characters referred to. Diabase and melaphyre occur near 
Kingswells, above Kinfauns. These rocks are simply altered 
basalt rocks. They consist essentially of plagioelase, augite, 
and olivine with magnetite: but the olivine usually is 
serpentinized and the augite also is generally more or less 
altered. A well-marked basalt-rock has long been quarried on 
the slopes at Corsiehill. 
These are the chief kinds of crystalline igneous rock met with 
in the hill itself. It is sometimes hard to say whether some of 
the fine-grained blue rocks should be classed with the porphy- 
rites or the basalt-rocks ; but although they sometimes closely 
approach the latter in character they seem to be most nearly 
related to the porphyrites, and to belong to the great class of 
audesitic lavas. 
2. Fragmental Rocks.— These consist of conglomerate, grit, 
sandstone, tuff, breccia, and tuffaceous grits, &c. The con¬ 
glomerates are made up of somewhat well-rounded stones, 
consisting of various porphyrites, commingled with which are 
fragments of quartzite, felsite, &c.— the whole being set in a 
matrix of comminuted felspathic matter. Sometimes the stones 
are arranged in well-marked layers : in other places little or no 
trace of bedding is visible. Such conglomerate passes laterally 
into coarse grit, aDd this shades off into sandstone, with which 
dull argillaceous shales are now and again associated. All these 
beds are evidently of aqueous origin: they have been derived 
from the degradation of the crystalline and fragmental igneous 
rocks with which they are interbedded. Frequently, however, 
the aqueous rocks now described seem to shade off laterally into 
rocks which have all the appearance of true tuffs. The rocks 
referred to consist of rudely-bedded masses, consisting of angular 
and subangular stones set in a matrix or ground-mass of com¬ 
minuted porphyrite. The stones have all the appearance of 
lapilli, and have been derived from the immediate neighbour¬ 
hood. They are, in short, bits of porphyrites. These tuffs vary 
in colour—(lull yellow, green, brown, red, and grey shades being 
common. They are best seen in the grounds of Kinfauns, where 
they are closely associated with conglomerate. [A much better 
locality for their study, however, is the slope of Friarton Hill, at 
and above the railway.] 
All the rocks now described, with the exception of the basalt 
of Corsiehill Quarry, belong to the Lower Old Red Sandstone 
formation ; and it now remains to describe briefly the geologi¬ 
cal structure of the ground. The structure could hardly be 
simpler. Kinnoull Hill is, in short, composed of a succession 
of bedded porphyrites and interbedded fragmental rocks, all 
of which dip gently towards north-west. 
The upper 600 feet of the hill consist chiefly of porphyrites, 
which are occasionally separated by thin beds of fragmental 
rocks—one very good example of which may be studied near the 
Dragon’s Hole and in the cliff-face above Lairwell. Here maybe 
seen a bed of conglomerate of rounded stones, some of which 
are about 2 feet in diameter. This conglomerate rests upon the 
scoriaceous upper surface of a porphyrite, and is overlaid by 
another bed of porphyrite—the bottom portion of which is like¬ 
wise scoriaceous, and in places abundantly charged with baked 
sandstone and mudstone. A very good section showing some of 
the interbedded sandstones and shales was exposed in "Witch- 
hill Quarry, which is now occupied by the Board School. The 
section is still partly exposed behind the school. 
To the overlying porphyrites, which form the upper portion, 
and indeed nearly all the surface of Kinnoull Hill, succeed thick 
conglomerates and tuffaceous beds which crop out underneath 
the great cliff. How thick these conglomerate beds are it is 
difficult to say. But they are probably not less than 250 or 300 
feet. They may be followed along the base of the great cliff to 
Kinfauns, and up the Deuchney Burn to near the saw-mills. 
Behind the Home-Farm they contain at least one intercalated 
sheet of porphyrite. It may be as well to note here that the 
tuffaceous beds which crop out in the railway cutting at the 
tunnel, near Nether Friarton, are on the same horizon as the 
conglomerates of Kinnoull and Kinfauns. On the slopes of the 
Friarton Hill they are well exposed, and alternate in that neigh¬ 
bourhood with beds of porphyrite; and possibly the same may 
be the case to some extent with the conglomerates underlying 
the porphyrites of the great cliff of Kinnoull: for in that 
neighbourhood the falls of debris hide the lower part of the 
section. 
It is obvious from the dip of the strata that the Kinnoull con¬ 
glomerates must be underlaid by porphyrite. The rocks forming 
Moncreiffe Hill are inclined towards the north-west and north, 
and without doubt continue across the Tay so as to underlie 
Kinnoull Hill. Taking the average inclination of the rocks at 
8 deg., or 1 in 7, we get the following thicknesses for the igneous 
and associated fragmental rocks of the hill:— 
Upper porphyrites with interbedded sand¬ 
stones and conglomerates,.600 feet. 
Conglomerate, tuffs, breccias, &c., lying at 
base of hill,.250 ,, 
Lower porphyrites (seen in Moncreiffe Hill), S00 „ 
1650 feet. 
HISTORICAL GEOLOGY OF KINNOULL HILL. 
It is impossible to read off the geological history of Kinnoull Hill 
without reference to the range of which it forms only an insignifi- 
caut part. I shall therefore simply state that an examination of 
the whole range leads to the belief that the porphyrites were 
erupted upon the floor of a large inland sea or lake, the northern 
shores of which were formed by the rocks of the Highland area. 
Over the floor of that ancient lake were deposited the red sand¬ 
stone of Strathmore, and the flags and shales with which the 
porphyrites are in many places interbedded. The igneous rocks 
seem in time to have formed low volcanic banks or hills rising 
above the level of the lake, in the waters of which the fragmental 
materials ejected from the old volcanic foci were winnowed and 
spread out in bedded layers. The coarse conglomerates seem in 
many places to indicate the action of torrential water. Probably 
the volcanic hills were subject here and there to the denuding 
action of streams and torrents which rolled the fragmental 
materials down into the lake, where they formed broad cone¬ 
like sheets. The general distribution of the conglomerates and 
their very irregular appearance—thickening and thinning out as 
