
278 

NATURE 

of the Carboniferous system between Nithsdale and Fife, and 
which I have shown to mark the position of volcanic orifices 
during Permian times, I am inclined to regard these later igneous 
rocks of Edinburgh as dating from the Permian period. Arthur’s 
Seat, however, seems to have been the only volcano in action 
during that period in this neighbourhood. 
There still remains for notice one further and final feature of 
the volcanic history of this part of Scotland. Rising indifferently 
through any part of the other rocks, whether aqueous or igneous, 
and marked by a singular uniformity of direction, there is a series 
of basalt dykes, which deserves attention. They have a general 
easterly and westerly trend, and even where, as in Linlithgowshire, 
they traverse tracts of basalt-rocks, they preserve their indepen- 
dence, and continue as readily separable as when they are found 
intersecting sandstones and shales. These dykes belong to that 
extensive series which, running across a great part of Scotland, 
the north of England, and the north-east of Ireland, pa-ses into, 
and is intimately connected with, the wide basaltic plateaux of 
Antrim and the Inner Hebrides. They date, in fact, from 
Miocene times, and, from their numbers, their extent, and the 
distance to which they can be traced from the volcanic centre of 
the north-west, they remain as a striking memorial of the vigour 
of volcanic action during the last period of its manifestation in 
this country. 
Glacial Phenomena 
To an eye accustomed to note the characteristic impress of ice- 
action upon a land-surface —the neighbourhood of Edinburgh 
presents many features of interest. It was upon Corstorphine 
Hill, on the western outskirts of the city, that Sir James Hall first 
called attention to striated rock-surfaces which, though erroneously 
attributed to the abrasion produced by torrents of water, were even 
then recognised as trustworthy evidence of the last great geolo- 
gical changes that had passed over the surface of the country. 
Even before we come to look at the surface in detail, and note 
the striation of its rocks, we cannot fail to recognise the distinc- 
tively ice-worn aspect of the hills round Edinburgh. Each of 
them is, in fact, a great roche moutonnée, left in the path of the 
vast ice-sheet which passed across the land. ‘That this ice was 
of sufficient depth and mass to override even the highest hills, 
is proved not merely by the general ice-worn surface of the 
landscape, but by the occurrence of characteristic strize on the 
summits of the Pentland Hills, 1,600 feet above the sea ; that it 
came from the Highlands, is indicated by the pebbles of granite, 
gneiss, schist, and quartz rock, occurring in the older boulder- 
clays which it produced ; and that, deflected by the mass of the 
southern uplands, the ice in the valley of the Lothians was forced 
to move seawards, in a direction alittle north of east, is shown by 
the trend of the striz graven on the rocks, as at Corstorphine, 
Granton, Arthur's Seat, and Pentland Hills. 
Connection of the present form of the surface with Geological 
Structure 
In concluding these outlines, let me direct the attention of the 
Section to the bearing which the geological structure of the dis- 
trict wherein we are now assembled has upon the broad and much 
canvassed question of the origin of land-surfaces. In the first 
place, we cannot fail to be struck with the evidence of enormous | 
denudation which the rocks of the district have undergone. 
Every formation, from the oldest to the latest, has suffered, and 
the process of waste has been going on apparently from the 
earliest times. We see that the Lower Silurian rocks were up- 
heaved and denuded before the time of the Lower Old Red 
Sandstone ; that the latter tormation had undergone enormous 
erosion before the beginning of the Carboniferous period ; that of 
the Carboniferousrocks, athickness more than 3.000 feet had been 
worn away from the site of Arthur’s Seat before the last eruptions 
of that hill, which are possibly as old as the Permian period ; that 
still further and vaster denudation took place before the setting in 
of the Ice-age ; and finally, that the deposits of that age have since 
been to a large extent removed. With the proofs, therefore, of 
such continued destruction, it would be vain to look for any 
aboriginal outline of the surface, or hope to find any of the later 
but still early features of the landscape remaining permanent 
amid the surrounding waste. 
In the second place, we note, that in the midst of this greatly 
denuded area, it is the harder rocks which form the hills and 
crags. Those masses which in the long process of waste pre- 
sented most resistance to the powers of destruction, are just those 
which, as we might expect, rise into eminences, while those whose 
resistance was least sink into plains and valleys. All the craggy 


heights which form so conspicuous a feature of Edinburgh and its 
neighbourhood, are composed of hard igneous rocks, the undu- 
lating lowlands lie upon soft aqueous rocks. 
In the third place, the coincidence of the position of hills and 
crags with the existence of ancient igneous rocks, cannot be mis- 
interpreted by inscribing the presence and form of the hills to the 
outlines assumed by the igneous material ejected to the surface 
from below. The hills are not due to igneous upheaval at all, 
but can be shown to have been buried deep under subsequent 
accumulations, to have been bent and broken with all the bend- 
ings and breaks these later formations underwent, and to have 
been finally brought to light again only after a long cycle of de- 
nudation had removed the mass of rock under which they had 
been concealed. What is true of the hills of Edinburgh, is true 
also of ali the older volcanic districts of Britain. Even where 
the hills consist of volcanic rocks, their existence, as hills, can be 
proved to be one of the results not of upheaval, but of denudation. 
In the fourth place, this district furnishes an instructive illus- 
tration of the influence of faults upon the external contour of a 
country. The faults here do not form valleys. Onthe contrary, 
the valleys have been cut across them in innumerable instances. 
Inthe Dalkeith coal-field, for example, the valleys and ravines of 
the river Esk traverse faults of 190 to nearly 500 feet, yet there 
is no inequality at the surface, the whole ground having been 
planed down by denudation to one common level. When, how- 
ever, a fault brings together rocks which differ much in their re- 
lative powers of resistance to waste, the side of the dislocation 
occupied by the harder rocks will tend to form an eminence, 
while the opposite side, consisting of softer rocks, will be worn 
down into a hollow or plain. Conspicuous examples are fur- 
nished by the faults which, along the flanks of the Pentland Hills, 
have brought down the comparatively destructible sandstones and 
shales of the Carboniferous series, against the much less easily 
destroyed porphyrites and conglomerates of the Old Red Sand- 
stone. 
In fine, we learn here as elsewhere in our country, and here 
more strikingly than often elsewhere, on account of the varied 
geological structure of the district, the present landscape has 
resulted from a long course of sculpturing, and that how much 
soever that process may have been accelerated or retarded 
by underground movements, it is to the slow but irresistible 
action of rain and frost, springs, ice, and the sea, that out of the 
various geological formations among which Edinburgh lies, her 
picturesque outline of hill and valley, crag and ravine, has, step 
by step, been carved. 


LETTERS TO THE EDITOR 
[Zhe Editor does not hold himself responsible for opinions expressed 
by his Correspondents, No notice ts taken of anonymous 
communications. | 
The New Psychic Force 
A YEAR ago Mr. Crookes, in a paper published in the 
Quarterly Fournal of Science, announced his intention of scienti- 
fically investigating a certain class of phenomena, then known as 
‘* spiritual,” which he complained had been strangely and un- 
warrantably neglected by those whose duty it was to investigate 
them. The results of some of these investigations have at last 
been published, in the same journal, under the title of ‘‘ An ex- 
perimental investigation of a new force.” 
Owing no doubt to the scientific reputation of Mr. Crookes, 
and the somewhat sensational title of the paper, it has attracted 
considerable attention. Whilst in quarters not purely scientific, 
much has been written about it, no attempt has been made, 
as far as I am aware, to subject the details of the experiment 
there described to a critical examination, It is the duty of every 
scientific man to be very anxious that nothing worthy of the name 
of Science, or calculated to be of permanent injury to Science, 
| should ever obtain general credence. Whilst far from saying that 
this will be the result of Mr. Crookes’ paper, still I must confess 
that it appears to me that, carried away by enthusiastic impulses, 
he has trusted to experiments which in matters more purely 
scientific than his investigations really were, he would never have 
relied upon without further and more searching examination, 
In the first place, then, scientific men will not, cannot admit 
the validity of a ‘‘new force” (of the nature of that which Mr. 
Crookes calls ‘‘ psychic ”) which rests merely on the results of 
two experiments made in the presence of three or four persons, 
