214 
acceptation of the view, that they were so, would go far 
‘to reconcile the discrepant opinions of the geologists and 
physicists. 
There is, as I learn, some slight geological reason for 
supposing the tides to have been higher in early times, 
although this interpretation does not seem to have been 
hitherto attributed to the fact to which I allude. It 
appears that in the oldest formations there are beds many 
feet in thickness covered with ripple marks. The preserva- 
tion of ripples is due to a fortuitous concurrence of causes, 
and it therefore cannot be asserted positively that if 
many ripples are preserved the number of ripples formed 
was great. Such a deduction possesses, however, a con- 
siderable degree of probability, and one of the conditions 
for the formation of many ripples is a great ebb and flow 
of the tides. 
Lyell’s interesting observations on the sands in the Bay 
of Fundy (“Travels in North America,” vol. ii. p. 166), 
where the tide rises through about seventy feet, seem to 
show that the preservation of superficial marks on sand 
occurs principally at neap tides, when large areas of sand 
are exposed for a long time to the sun, after having been 
covered with water at the spring tide. Now when the 
tides were twice as high as at present, there must have 
been 19 or 20 of our present days in the month instead 
of 27} as at present, and there would be about 38 neap 
tides in the year instead of about 26. 
Since writing the above I have seen Mr. Hull’s paper 
on this subject in NATURE (vol. xxv. p. 177). The evi- 
dence which he adduces is of much interest, and if geo- 
logists should generally come to recognise the necessity of 
a powerful denuding agency in order to explain the earlier 
geological phenomena, such an opinion will stand in direct 
confirmation of the theory which I have advanced. Not- 
withstanding what Mr. Hull says, I am still inclined to 
adhere more to the moderate views maintained above, 
rather than to admit the extended application of the tidal 
theory to geology for which Mr. Ball contends. I con- 
ceive that a very great acceleration of geological action 
would result from tides of even one-hundredth of the 
height portrayed by Mr. Ball, when such tides are 
accompanied by an intensification of meteorological 
action. 
If Mr, Hull had read my papers, he would have seen 
that a necessary concomitant of these changes has been 
a secular diminution of the ellipticity of the earth’s 
figure. For example, when the tides were 600 feet in 
height, the ellipticity must have been about twelve times 
as great as at present. Now Sir William Thomson will 
not allow that there can have been any great change in 
the ellipticity of the earth’s figure since the consoli- 
dation of the earth (Thomson and Tait’s “ Nat. Phil.” 
§ 830). 
If this opinion is correct, extended geological action, as 
resulting from the present series of causes, is absolutely 
excluded. For myself I am not at present able to see 
the force of his argument, for various reasons on which 
it is useless to enter here. But it must be admitted that 
in any contest between him and me the chances of 
correctness are enormously on his side. 
In conclusion I wish to add that in my first paper I 
probably attributed too much of the changes in the con- 
“NATURE 
| (Yan. 5, 1882 
tidal deformation of the earth’s mass. The evidence is 
strong that such tides are now but small, or even scarcely 
sensible in amount, and accordingly in all probability the 
later part of the changes must be attributed almost en- 
tirely to the effects of oceanic tidal friction, whilst in the 
earlier part the tides of the solid or semi-solid matter 
constituting the planet were the more important. It is 
remarkable that this view enables us to give a satisfactory 
account of the inclination of the lunar orbit to the ecliptic, 
as is shown in a later paper.! 
G, H. DARWIN 
EXNER ON CEREBRAL LOCALISATION 
Untersuchungen tiber die Localisation der Functionen in 
der Grosshirnrinde des Menschen. Von Prof. Sigmund 
Exner. (Wien, 1881.) 
E [as work is an attempt to determine the functions of 
different parts of the cerebral hemispheres by an 
examination of the facts of disease alone, independently 
of physiological experiment. The difficulties which have 
to be encountered in the solution of the problem by this 
method are great, and the sources of fallacy numerous. 
The facts, collected as they must be from the most 
diverse sources, are not all of the same value, and errors 
of observation on the score of inaccuracy or incomplete- 
ness have to be taken into account and allowed for. The 
experiments of disease are as a rule rude, and the condi- 
tions highly complex. Certain parts of the brain are more 
liable to disease than others, and one hemisphere more 
than the other. Besides the lesion actually discovered 
after death, there may be others not discovered or not 
discoverable by our present methods, either coincident 
merely or indirectly connected with the visible lesion ; for 
morbid anatomy and morbid physiology are by no means 
coextensive. Exactly symmetrical bilateral lesions are 
extremely rare in disease, and yet such facts are abso- 
lutely necessary for the decision of many important 
questions. 
These and many other circumstances render the deter- 
mination of the functions of the brain from the data of 
disease alone extremely uncertain, if not impossible. 
Until the discovery of new experimental methods a few 
years ago cerebral pathology, except in one or two par- 
ticulars, chiefly speculative or purely empirical, was 
practically in a state of chaos. It is only since the 
introduction of the new doctrines founded on experi- 
mental research that the facts of cerebral disease have 
begun to be investigated and recorded with any approach 
to scientific accuracy, and order has begun to show itself 
where formerly all seemed confusion. 
Prof. Exner is of opinion that his predecessors have 
examined the facts of cerebral disease merely with a view 
of confirming preconceived theories, and have not exer- 
cised sufficient discrimination in the selection of the cases 
they adduce in favour of the propositions they maintain. 
In this respect particularly he claims superiority over all 
who have treated the subject before him. 
Out of several thousand cases of cerebral disease on 
record, he has been able to find only 168 instances of 
* “On the Secular Changes in the Elements of the Orbit of a Satellite, 
figuration of the earth and moon to the effect of bodily | &c.,"" (Phil. Trans., part it., 1880, p. 731). 
