388 
NATURE 
| March 16, 1871 

towards the partial adoption of a chronological classification, 
founded, no doubt, on the prevailing belief in an essential 
difference between the ‘‘ plutonic” and °‘‘ volcanic” rocks, and 
on the notion that the age of such rocks may be determined by 
their mineral constituents, just as sedimentary deposits may be 
recognised by their included fossils. The microscopical exami- 
nation of many hundred thin sections of the older melaphyres 
and more recent basalts establishes the fact that no such 
essential difference exists, but that, on the contrary, the same 
minerals are the constituents of both ; a difference there undoubt- 
edly is, but the microscope shows that it has been produced by 
chemical action operating under more or less favourable circum- 
stances during long periods of time. Numerous specimens of 
the so-called melaphyres from the coal-fields of Scotland and the 
midland counties are unquestionably composed of the same 
constituent minerals as the tertiary basalts from the coast of 
Antrim, Auvergne, and the Rhine. 
On comparing the least altered portions of the older rocks with 
some of the basalts, no difference whatever is observable ; tri- 
clinic felspar, magnetic oxide of iron, augite, and olivine are the 
chief ingredients of both, The latter mineral has been regarded 
as characteristic of the more recent basalts, but, as I have shown 
elsewhere, * it exists quite as frequently in the melaphyres. 
The fact, however, on which it is most important to insist, and 
which has not hitherto been recognised, is that the difference 
now existing between old melaphyres and recent basalts is due to 
chemical action subsequently to the formation of the rocks ; not 
only have most of the amygdaloids been thus formed, and 
numerous microscopic cavities filled up, but the felspar is fre- 
quently much altered, and pseudomorphs of olivine, augite, and 
hornblende have been formed ; thus producing a marked change 
in the colour and hardness of the rock. Pseudomorphs of oli- 
vine are the most abundant, and are of great interest, as crystals 
in various stages of alteration may frequently be observed. 
Prof. Zirkel has shown that in some basalts the various con- 
stituents have crystallised firmly together, and lie in actual con- 
tact with each other without any intervening cement, while in 
other cases there is an amorphous glassy substance in which they 
are embedded. Precisely the same facts may be observed in many 
melaphyres, and notably so in some of the rocks from the Glas- 
gow coal-field. Many of these rocks from the Scottish car- 
boniferous strata are of great importance in these investigations, 
as their age has been satisfactorily determined by the valuable 
labours of Mr. Geikie and his brother. 
In revising the nomenclature, it will be for petrologists to decide 
whether or not two rocks originally of identical composition 
should receive different names because one has undergone a cer- 
tain amount of alteration. In most cases there is undoubtedly a 
difference in their appearance, and it might be convenient to re- 
cognise the fact in the nomenclature ; but Mr. Geikie’s anticipa- 
tion that ‘‘there is such an insensible gradation that no sharp 
line can be drawn between them” will certainly have to be re- 
cognised, 
If this method of microscopical analysis is carefully carried out 
on a sufficiently extensive scale, there can hardly be a doubt that 
we shall soon acquire a more satisfactory knowledge of all the 
older rocks ; some little has already been done with the mela- 
phyres, and I hope shortly to submit the results to the judgment 
of those interested in the subject. S. ALLPORT 

Tin 
THE discussion of the isolation of St. Michael’s Mount subject 
has now branched off into a subsidiary question, which should 
not pass unnoticed, A writer dwelling on the abundance of tin 
found in Britain, argues that this natural product of our soil has 
given a name to our island home. I have met with this sugges- 
tion elsewhere, but have never been able to accept it. Our word 
vin is of comparatively modern formation. The Welsh word is 
ystaen, which corresponds so closely with the Latin stannum as 
to lead to the inference that the one form is derived from the 
other, although we may not be able precisely to say which is the 
elder of the two. 
Now, ali things being equal, our modern word iz might be 
accepted as a corruption of either of the above forms; but that 
it really is more nearly allied to the Teutonic forms of the same 
word, as found in Saxon, Danish, German, Swedish, &c., all 
being equally traced to a primitive root preserved in the Sanscrit 
word faz, 
* Geol. Mag. vol, vii. p. 159. 
It will thus appear almost certain that our word ¢iz is of 
Teutonic origin, and not used in this island so early as the argu- 
ment for its forming a particle of the word Britain requires. My 
objection being thus stated, that the word # is a comparatively 
modern word with us, if of Teutonic origin; yet, on the other 
hand, if it be assumed as a plausible corruption of the Welsh 
ystaen, or the Latin stannum, it appears to me that the primitive 
words for Britain ought to be found spelt in such variety of form 
as to lend some countenance to this idea, if it he really founded 
on fact. But it is not so; consequently we must not indulge the 
fancy that that useful metal ‘‘tin” has any place in the construc- 
tion of the word Britain. Nae > 



PAPERS ON IRON AND STEEL 
No. II].—THE BESSEMER PROCESS*—(continued ) 
I ETURNING to the Bessemer flame, we now reach 
what I have described as its second stage, when its 
dimensions and brilliancy reach their maxima. We know 
that carbon must be burning there, and in no small 
quantity. The average of above three per cent. shown in 
the analyses, gives in a charge of six tons more than 
3°6 cwt. of carbon, requiring for its complete combustion 
into carbonic acid nearly half a ton of oxygen, or about two 
tons of atmospher cc air. There need be a mighty roar to 
pour forth all this, and the 14cwt. required for the silicon 
in the course of about twenty minutes. An interesting 
problem now presents itself in the whiteness and brilliancy 
of the flame. It is totally different from the carbonic 
oxide flame which is produced by the combustion of carbon 
per se. Whence comes this whiteness? Is it due to the 
combustion of iron in addition to that of carbon, to solid 
particles of carbon, or is there any important quantity of 
hydro-carbon present ?} The latter explanation is forcibly 
suggested by the appearance of the flame, and is, I think, 
to some extent, confirmed by the spectroscope. There is 
still, however, some red smoke above the flame, which, 
though less abundant now than in some other stages of 
the blow, is sufficient to indicate that some iron is burning, 
probably small particles mechanically ejected into the 
flame by the force of the blast. 
It is during this period of the blow that the lines which 
have been figured and described by Dr. Watts and Dr. 
Roscoe as the spectrum of the Bessemer flame are most 
distinctly displayed. This spectrum includes some of 
the iron lines, the lines of lithium.{ sodium, and.potas- 
sium, and the red band of hydrogen seen as a black 
band, besides the very complex series of lines which 
have been designated “the carbon lines” of the 
Bessemer flame. These lines probably include a 
hydro-carbon sp. ctrum,—I say “ probably,” because they 
do not exactly correspond with the hydro-carbon spectra 
with which they have already been compared. Nitrogen 
lines are also displayed, but whether these are due to 
cyanogen, or to any other compound including carbon and 
nitrogen, has not yet been determined. What then is the 
particular compound of carbon which is burning in the 
Bessemer flame? Js it a hydrocarbon, and if so, with 
which of the many known varieties of hydro-carbon does 
it correspond? Do the nitrogen lines belong to any 
compound of nitrogen whose spectrum may be identified ? 
These are questions of consideiable philosophical and 
practical interest which, I think, the spectroscope may be 
made to answer. Hitherto, the spectroscopic investigations 
* We regret that, owing to the pressure on our space, we have been com- 
pelled to keep this article, and the one printed last weck, in type for some 
weeks ; similar conclusions have in the meantime been arrived at by other 
observers. —Ep. 
+ I speak of solid particles of carbon as quite adistinct case from hydro- 
carbon flame, believing in the soundness of Frankland’s conclusion that the 
brilliancy of a hydro-carbon flame is of due to the combustion of solid 
particles of carbon. My own experiments on the transparency of the zw/rfe 
portion of common coal gas flames strongly confirm Dr. Franklana’s view. 
t I have only found the lithium occasionally. In many instances I have 
watched a blow fiom beginning to end without observing any appearance ot 
the red lithium band which, when seen at all, is so unmistakeably brilliant. 
— 
