458 
placed in our hands by the researches of the American geo- 
logists. 
an Northern Europe, Kjerulf, Dahll, Brogger, Reusch, and 
other geologists have ably illustrated the same peculiarities of 
structure in the denuded mountain-chain near the southern ex- 
tremity of which we are now assembled ; and in a recent valu- 
able and suggestive essay ‘‘On the Secret of the Highlands ” 
Professor Lapworth has shown how perfectly these structures 
are exemplified in the western district of Sutherland. 
In offering a few remarks on some of the still unsolved prob- 
lems of Highland geology I shall not hesitate to treat, as be- 
longing to the same geological district, both Scandinavia and 
Scotland. Not only is the succession of geological deposits in 
the two areas almost completely identical, but the characters 
of the several formations and their relations to one another in the 
one country are almost the exact counterpart of what they are 
in the other. 
The problems which await solution in Scotland are the same 
which confront our brethren in Scandinavia ; their difficulties 
are our difficulties, their successes our successes ; if they share 
the benefits of our discoveries, we equally partake with them in 
the fruits of their achievements. Important links in the chain 
of geological evidence, absolutely wanting in the one area, may 
perchance be found in the other. Every advance, therefore, 
which is made in the knowledge of the rocks of the one country, 
must necessarily re-act upon the opinions and theories which 
prevail among geologists in the other. 
At the base, and forming the foundation of this greatly 
denuded mountain-chain, there exist enormous masses of highly 
foliated, crystalline rocks. These, in great part at least, under- 
lie the oldest known, fossiliferous strata, and are therefore of 
pre-Cambrian or Archzean age. In spite of the labours of 
Kjerulf, Dahll, Brogger, Reusch, Tornebodhm, and many others 
in Scandinavia, and of Macculloch, Nicol, and their succes- 
sors in this country, much still remains to fbe done in studying 
the petrographical characters and the geognostic relations of 
these widespread formations. 
Some thirty years ago it was suggested by Sir Roderick 
Murchison that among these Archzean rocks there exists a 
“* fundamental gneiss,” a formation which is the counterpart and 
contemporary of the rocks in Canada, to which Sir William 
Logan gave the name of ‘‘ Laurentian.” Since that time other 
similar attempts have been made to identify portions of these 
Archean rocks in the Highlands and Scandinavia with crys- 
talline rock-masses in different parts of the New and Old 
World. 
I confess that, speaking for myself, I am not sanguine as to 
the success of such endeavours. The miserable failures which 
we have seen to have attended similar attempts, in the case even 
of far less altered rocks, where identifications have been based 
on mineralogical resemblances only (and in connection with 
which definite paleontological or stratigraphical evidence has 
been subsequently obtained) ought surely to teach us caution in 
generalising from such uncertain data. It has been argued that, 
where palzeontological evidence is wholly wanting, and strati- 
graphical relations are doubtful or obscure, then we may be 
allowed to avail ourselves of the only data remaining to us— 
those derived from mineralogical resemblances. But surely, in 
such cases, it is wiser to admit the insufficiency of the evidence, 
and to say ‘‘ We do not know!” rather than to construct for 
ourselves a ‘‘fool’s paradise,’ with a tree of pseudo-knowledge 
bearing the Dead-Sea fruit of a barren terminology! The 
impatient student may learn with the blind poet that 
‘They also serve, who only stand and waits 
It is thought by some that the application of the microscope 
to the study of rock-masses may reveal peculiarities of structure 
that will serve as a substitute for paleontological evidence con- 
cerning the age of a rock when the latter is wanting. Greatly 
as I value the insight afforded to us by the microscope when it is 
applied to the study of the rocks, and highly as I esteem the 
opinions of some of those who hold these views, yet I fail to see 
that any such connection between the minute structure and the 
geological age of a rock has as yet been established. 
Although the bold generalisation which sought to sweep all 
the crystalline rocks of our central Highlands into the great 
Silurian net has admittedly broken down, yet it by no means 
follows that the whole of these rock-masses are of Archzean age. 
Nicol always held that among the complicated foldings of the 
Highland rocks many portions of the older Palzeozoic formations, 
NATURE 
[| Sept. 10, 1885 
in a highly altered condition, were included (see Quart. Journ. 
Geol. Soc. vol, xix. (1864), p. 184, and ‘* Geology and Scenery 
of the North of Scotland,” 1866). The same view has been 
persistently maintained by Dr. Hicks, to whose researches among 
the more ancient rock-masses of the British Isles geologists are 
so greatly indebted, and also by Prof. Lapworth. 
To. the settlement of this very important question we may feel 
sure that the effort of the officers of the Geological Survey will 
be especially directed. The geological surveyors of Scandinavia 
have been so fortunate as to detect, in rocks of an extremely 
altered character, a number of fossils sufficiently well preserved 
for generic and sometimes even for specific identification. Fail- 
ing the occurrence of such a fortunate accident, I confess that it 
has always appeared to me that the disturbances to which these 
Highland rocks have been subjected are so extreme, and the dif- 
ficulty of making out the original planes of bedding so great, 
that but little can be hoped for from general sections constructed 
to show the relations of the rocks of the Central and Southern 
Grampians to the fossiliferous deposits of the North-West of 
Sutherland. 
Lying unconformably upon these Archzean crystalline rocks in 
our North-West Highlands we find great masses of arkose or 
felspathic grit, with some conglomerates, the whole of these 
well-stratified deposits attaining a thickness of several thousands 
of feet. These rocks, in their characters and their relations, so 
greatly resemble the ‘‘Sparagmite Formation” of Scandinavia, 
that it is impossible to refrain from drawing comparisons between 
them. The Scandinavian formation, however, includes calcareous 
and slaty deposits, which are wanting in its Scottish analogue. 
The ‘‘Sparagmites” of Scandinavia, as a whole, appear to 
underlie strata containing Cambrian (Primordial) fossils, but in 
the very highest portion of the “‘ Upper Sparagmite Formation ” 
of Southern Norway there have been found, according to Kjerulf, 
specimens of Paradoxides. 
The Scottish formation has, on the other hand, yielded no 
undoubted organic remains. Murchison, on the ground of its 
unconformable infraposition to his Silurian strata, and its resem-" 
blance to certain beds in Wales which he called Cambrian, re- 
ferred it in his later years to that system. Although an identifi- 
cation, based on such grounds, must be admitted to be of small 
value indeed, yet the discovery of ‘‘ Primordial” fossils in the 
very similar rocks of Scandinavia may be admitted to lend it 
some slight support. In the present state of our knowledge, 
however, it is surely wiser to admit that the question of the age 
of these beds is still an open one, and to call it by the name 
suggested by Nicol—‘‘ The Torridon Sandstone.’”’ Kjerulf be- 
lieves there is evidence that the Scandinavian Sparagmite, in 
places, passes horizontally into true gneiss, and similar appear- 
ances are not wanting in the case of our Torridon Sandstone. 
(Zo be continued.) 
NOTES FOR THE OPENING OF A DISCUSSION 
ON ELECTROLYSIS, TO BE HELD IN 
SECTION B, AT THE BRITISH ASSOCIA- 
TION IN ABERDEEN, SEPT., 1885, BY 
PROFESSOR OLIVER LODGE 
I. [WHAT is an Electrolyte? The question has two distinct 
meanings : 
(2) Is a given substance an electrolyte at all ; ze. when 
alone. 
(é) Is it the electrolyte in any particular case ; z.e. when 
mixed with other substances. 
In answering (a) remember that the fact of bad conductivity 
does not imply that what there is is non-electrolytic. An 
electrolyte is one whose conduction is wholly electrolytic. 
Distinction between metallic - and electrolytic conduction. 
Obedience to Ohm’s law shown by electrolytes. 
Tests of Electrolytic conduction, 1%. Visible decomposition. 
2. Polarisation, 
3. Non - agreement 
Volta’s series-law. 
4. Transparency. 
In answering (4) the fact of bad conductivity gives a decided 
negative, but substances which almost insulate when alone may 
conduct when mixed ; e.g. H,O + HCl. 
To the question, What is the real conductor when a salt (or 
acid) is dissolved in water? there are four possible answers : 
with 
- 
