66 
NATURE 
| May 22, 1873 
sense and reasoning power which I believe them to possess, and 
also to the assumption that in the case supposed they would 
recollect merely the odours, not the objects the presence of which 
these odours had indicated. I imagine that animals know, just 
as well as we do, that some sights, sounds, and smells are caused 
by permanent, others by evanescent or changeable causes. The 
smell or sound of a flock of sheep would indicate to a dog the 
presence of an actual flock of sheep, just as surely as the sight of 
them would do, and he would no more lose his way because 
those sheep were not in the same place the next day or the next 
week, than he would had he travelled the road on foot with his 
eyes open. The smell of a wood, of a farmyard, of a ditch, a 
village, or a blacksmith’s shop, with the more or less charac- 
teristic sounds accompanying these, would tell the dog that cor- 
responding objects were there just as surely as the sight of them 
would do. Onhis return he would recognise the objects, not 
the smells and sounds only, and he would be no more puzzled by 
the absence of certain moveable objects he had recognised by 
smell than he would be had he seen them. I quite. believe that 
mistakes would often be made owing to the discontinuousness of 
sufficiently characteristic odours ; but the process of ‘trial and 
error,” suggested by F.R.S., would be constantly used, and this 
is in accordance with the length of time usually taken in these 
journeys, often very much longer than would be required for a 
return by the shortest route and at moderate speed. 
. A friead has communicated to mea most remarkable fact, of 
a different character from any which have been referred to dur- 
ing the course of this discussion ; and as I have it at first hand 
and took the exact particulars down as narrated to me, I think 
it will be cf value. Many years ago, my friend lost a favourite 
little dog. He was then living in Long Acre. Three months 
after, he removed to a house in another street about half a mile 
off, a place he had not contemplated going to or even seen 
before the loss of the dog. Two months after this (five months 
after the dog was lost) a scratching was one day heard at the 
door, and on opening it the lost dog rushed in, having found out 
its master in the new house. My friend was so astonished that 
he went next day to Long Acre to an acquaintance who lived 
nearly opposite the old house (then empty) and told him his little 
dog had come back. *‘Oh,” said this person, ‘‘I saw the dog 
myself yesterday. He scratched at your door, barked a good 
deal, then went to the middle of the street, turned round several 
times, and started off towards where you now live.” My friend 
cannot t:ll, unfortunately, what time elapsed between the dog's 
leaving the old and arriving at the new house. If every move- 
ment of this dog could have been watched from one door to the 
other, much might have been learnt. Could it have obtained in- 
formation from other dogs (and that dogs can communicate in- 
formation is well shown by Mr. A. P, Smith’s anecdote in your 
issue of three weeks back)? Could the odour of persons and 
furniture linger two months in the streets? These are almost the 
only conceivable sources of information, for the most thorough- 
going advocates for a ‘‘sense of direction” will hardly maintain 
that it could enable a dog to go straight to its master, wher- 
ever he might happen to be. 
Not to trespass further on your space, I would venture to hope 
that some persons, having means and leisure, would experiment 
on this subject in the same careful and thorough way that Mr. 
Spalding experimented on his fowls. The animals’ previous 
history must be known and recorded ; a sufficient number of ex- 
periments, at various distances and under different conditions, 
must be made, and a person of intelligence and activity must 
keep the animal in sight, and note down its every action till it 
arrives home. If this is done I feel sure that a satisfactory theory 
will soon be arrived at, and much, if not all the mystery that 
now attaches to this class of facts be removed. 
ALFRED R. WALLACE 
The Origin of Volcanic Products 
THAVE not yet had the advantage of seeing Mr. Mallet’s trans- 
lation of Palmieri’s late work on Vesuvius, but have read with 
interest Mr. Forbes’s review thereof and Mr. Mallet’s reply in 
Nature of Feb, 6 and March 20. I have no desire to enter 
into a controversy, but as I have for the past fifteen years taught 
and defended a theory of the origin of volcanic products identical 
with that now maintained by Mr. Mallet, I may be permitted to 
say afew words. That the source of all such matters was to be 
found not in the earth’s nucleus but in sedimentary strata, was 
taught by Referstein in his Maturgeschichte des Erdkorpers, in 
1834; and again, doubtless independently, by Sir J. F. W. 
Herschel in 1837 ; while, for my own part, I was led to the 
same conclusion before I became aware of the views of either of 
my predecessors, solely from a consideration of the varying 
composition of plutonic rocks and of the stony and vaporous 
products of volcanic action. To the views of Herschel I first 
called attention in the Canadian Fournal for March 1858, and 
again in the Quar. Geol. Fourn. for November 1859, pp. 488- 
496, § vii.). 7 ; 
In the first of these I haye said : ‘If we admit that all igneous 
rocks, ancient plutonic masses, as well as modern lavas, have 
their origin in the liquefaction of sedimentary strata, we can at 
once explain the diversities in their composition. We can also 
understand why the products of volcanoes in different regions are 
so unlike, and why the lavas of the same volcano vary at diffe- 
rent periods. We find an explanation of the water and carbonic 
acid, which ar: such constant accompaniments of volcanic 
action, as well as the hydrochloric acid, sulphuretted hydrogen, 
&c.” The nature of the reactions between siliceous, calcareous, 
and aluminous strata, holding carbonaceous matter, um, sea- 
salt, &c., was then discussed, and the products of their transfor- 
mations under the influence of water at an elevated temperature 
considered. In both of these papers referred to, the inadequacy 
of the views of Phillips, Durocher, and Bunsen, to explain the 
origin of these various products, was maintained. we 
In the Geological Magazine for June 1869, I returned to this 
subject in a paper on ‘* The Probable Seat of Volcanic Action,” 
where, after repeating and enforcing the above views, I said : 
“Two things become apparent from a study of the chemical 
nature of rocks ; first; that their composition presents such yaria- 
tions as are irreconcileable with the simple origin generally 
assigned to them ; and second, that it is similar to that of the 
sedimentary rocks whose history and origin it is, in most cases, 
not difficult to trace.” In what follows I endeavour to show in 
the latter the source of such ‘‘eruptive rocks as peridolite, 
phonolite, leucitophyre, and similar rocks, which are so many 
exceptions in the basic group of Bunsen.” 
Mr. Mallet has, however, madea very important advance in 
this theory of volcanic action by pointing out a source of heat 
independent of the cooling nucleus. Referstein had supposed 
heat to be generated by chemical action in the sediments, and 
his view has lately been brought forward, in a modified form, 
by Leconte ; but this I have always rejected as untenable. The 
chemical actions supposed to be involved in the processes would 
consume rather than generate heat. I have hitherto followed 
Herschel and Babbage in regarding the heat as directly derived 
by conduction from an incandescent nucleus, but Mr. Mallet has 
now shown that the work expended in the crushing of the strata 
which takes place in certain regions of the globe where the con- 
traction which attends the slow refrigeration ot the globe is dis- 
played in corrugations of the crust, is more than adequate to 
explain volcanic heat. To this it must be added that, inasmuch 
as the crushing process takes place in strata which, from their 
depth, are already at an elevated temperature, the heat developed — 
by the mechanical process comes in to supplement that derived 
by conduction from the igneous centre. Vose had already, in a 
general manner, pointed out thesame thing, suggesting in terms 
which are, it is true, wanting in scientific precision, the notion 
that the mechanical force at work in the crushing of the strata 
was the source of heat. This, however, in no way detracts from 
the great merit of Mr. Mallet, who may rightly claim “‘to have 
been the first to apply weight, measure, and number to volcanic 
theory,” and we await with great interest the publication of his 
quantitative results. Apart from his thermo-dynamic theory, 
however, his views of volcanic action are apparently identical 
with those of Referstein and Herschel, to which I have for 
many years been endeavouring to give form and consistency. I 
may here call attention to a paper, ‘‘On some Points of Dyna- 
mical Geology,” published in the American Fournal of Science 
for this month (April 1873), in which I have already alluded to 
the foregoing questions, and to the endeavours which I have for 
filteen years been making “to reconstruct the theory of the earth 
on the basis of a solid nucleus.” I have there rehearsed the 
views which I have all this time maintained as to the causes 
which determine the process of corrugation of the earth’s crust, 
the accumulation of sediments, and the development of volcanic 
activity in certain regions of the earth ; thus giving a theory of 
the geological and geographical distribution of past and present 
volcanoes. T. Srerry Hunr 
Institute of Technology, Boston, Mass., April 25 ve 
