368 

of structure consisting of small parts of canals filled with the 
dark colouring matter of the limestone,” and in only ‘‘a few 
rare instances ” are detected ‘‘ with a higher power in the margin 
of some of the septa traces of the fine tubulation characteristic 
of the chamber wall of Eozodn.” 3rd. It is almost an isolated 
example, and the measure of the metamorphism of its matrix 
together with its character—organic or otherwise—(from its 
generally doubtful nature as shown by Dr. Dawson’s own descrip- 
tion) could only be ascertained and settled by independent inquiry. 
I may also here observe that other cases of “chambers and 
canals stated to be injected with calcite appear to me to be of a 
no more reliable character. If, indeed, we accept the Tudor 
specimen and Madoe fragments as Eozo6n, why refuse this term 
to the Skye specimens which apparently possess the true features 
(chamber casts and nummuline layer) in a much more marked. 
manner? As regards imitative forms, Dr. Dawson and myself are 
in agreement, excepting that I must contend, from all the facts we 
are acquainted with, that a// Eozoénal forms are imitative, and 
not merely those that the exigencies of the discussion demand 
looked at from the organic stand-point. 
Respect for your space prevents me going into further details, 
but I may be permitted to suggest that the truth of the matter in 
no way hinges upon the possibility of comprehending the con- 
structive pseudomorphic theories advanced by King and Rowney. 
In what way though, excepting by pseudomorphism, I would 
ask, does Dr. Dawson account for the presence of the zmzilative 
forms which he thinks have confused other observers? And if 
we believe pseudomorphism to have originated them, why is it so 
trying to our faith to consider Eozoén Canadense to have been 
formed in the same manner? The fact is, chemical geology and 
the replacement and alteration of minerals—occurring as they do 
i1 the forms of other minerals—have been little studied by palzeon- 
tologists, or probably Eozobn might have remained ‘“* uncon- 
structed” to this day. It is well known that not only do 
minerals assume by replacement the crystalline forms proper to 
the mineral replaced, but also amorphous shapes filled with one 
mineral may be replaced by another without in any way destroy- 
ing the original form. 
There can be no doubt that a little knowledge of this kind 
would have infused the necessary caution, and have prevented 
anyone accepting as a fossil that which required the invention of 
a method of chemical deposition (excepting in these pages) 
hitherto unknown in nature. Serpentinous marble, as we may 
ascertain from all sources, is the typical Eozoénal. rock, and, 
though the minerals filling the so-called chambers and canals 
may be Loganite or pyroxene, in addition to the serpentine, they 
are intimately related in a pseudomorphic point of view. 
Loganite and serpentine, as I have before stated, are both pro- 
ducts of alteration. The organic hypothesis demands that we 
should consider the infilling to be, as contended for by Dr. T. S. 
Hunt, the same mineral originally supposed to be deposited therein. 
If this be so, then what becomes of the meaning of metamor- 
phism? ‘This to me is a trial of faith greater even than the 
acceptance of King and Rowney’s “ constructive criticisms.” 
Lawait with interest the publication of the papers sent to the 
Royal Irish Academy by Dr. Dawson and his colleague, Dr. 
Hunt, and trust they may contain new matter for consideration, 
as my only object has been to elicit further evidence, if there be 
any, in favour of the organic hypothesis. 
Feb. 17 T. MELLARD READE 
Ocean Currents 
IN reference to Mr. Laughton’s letter in NATURE of the 23rd 
of February, I must admit that the question of the movement of 
barometric depressions was not introduced into my first letter, 
for the reason that I did not anticipate the objection of a state 
of equilibrium which he raised, since the average differences of 
pressure only were dealt with ; but I do not see that it necessi- 
tates a change of ground to show how this difficulty is met by the 
variations which occur in the region of lower average pressure, 
and how these changes themselves, taking place in a certain line 
of movement, might affect the surface currents of the ocean ; and 
I am not disposed to accept the sweeping rejection of the whole 
power of differences in the atmospheric pressure, permanent or 
moving, which is contained in the last paragraph of the letter 
referred to, until more extended observations shall show what 
directions the great movements of changing pressure take in 
passing over the parts of the ocean which lie outside of the trade 
wind regions. } 
NATURE 


[March 9, 1871 
The action of a barometric depression in moving over the sea 
differs entirely from that of the winds in this, that by the former 
the level of a large area of the ocean surface may be raised and 
carried along with the depression round which the winds blow, 
whilst by the force of the latter the waters can only be drifted at 
the same level before the wind. 
I have been particularly careful to suggest difference of 
atmospheric pressure only as a supplementary power in the pro- 
duction of ocean streams, not as a chief one, and it was indeed 
the partiality of the various theories of the causes of currents 
which led me to open the subject at all. 
That the trade winds have a very large share in originating the 
Gulf Stream is undoubted, but that they can account for the 
whole of the phenomena of ocean currents, as Mr. Laughton” 
maintains, appears more than doubtful. 
The existence of the under outflowing current of the Mediter- 
ranean, corresponding to the inflowing surface stream, has been 
abundantly proved by the recent Government expedition under 
Dr. Carpenter. If this current be due to the action of the winds 
alone we should expect to find the direction of the upper and 
under streams reversed with a change of wind to opposite points 
east or west in the Strait. But the observations on the direction 
of the winds for six years at Gibraltar show that westerly winds 
(from N.W., W. and S.W.) prevail there for 198 days in the 
year, and easterly winds (N.E., E., and S.E.) for 144 days; 
further it happens that in the months of July, August, and Sep- 
tember, in one of which the observations on the outflowing under- 
current were made, east winds prevail in the ratio of two days to 
one day of west wind. Experiments similar to that used to, de- 
termine the presence of an under-current in the Strait of Gibral- 
tar, have been made in the open ocean, and Maury (at p. 206 of 
the gth edition of his work) quotes an instance of an apparatus 
constructed of a block of wood, sunk by weights to 500 fathoms, 
and attached by a line to a small floating barrel, having moved 
off ‘‘against wind and sea, and surface current.’’ ‘he members 
of the late German Arctic expeditions have observed that where 
the warmer blue waters moving from south-westward meet the 
impure waters of the Spitzbergen and east Greenland current, 
there is a definite line of demarcation which would indicate that 
the Atlantic water here dips down beneath the specifically 
lighter water of the ice-bearing current, a conclusion which is 
sipponet by the increase of temperature with the depth beyond 
this point. 
Such under-currents can in no way be primarily caused by 
the action of the winds, and if difference of temperature and 
density must be called in to account for them, it must be admitted 
that these causes have to do with the upper streams also. 
I would take this opportunity to correct a statement made in 
my second letter, of a probable movement of a barometric de- 
pression across the British Isles at the rate of ninety miles an 
hour. The depression there referred to appears to have had 
an oblong form, the longer axis moving nearly parallel to the 
length of the British Isles from N. to S., so that the record of 
its passage took place at Valentia and at Aberdeen within a 
short interval of time, thus giving an apparently great rate of 
travelling. But I have the authority of the Secretary of the 
Meteorological Office for the facts given beneath, which prove 
that a rate of depression movement of upwards of seventy 
English miles an hour may take place. On the 16th of Decem- 
ber, 1870, a minimum reading of the barometer was registered 
at Valentia at 2" 45" P.M. ; at Kew, at 95 30™ p.m.; at Yar- 
mouth, at 10" p.M., where the mercury remained at the same 
level for four hours. The interval of time between the registra- 
tions at Valentia and Yarmouth is 7" 15™; the distance between 
these places is 520 miles. It seems probable also that the centre 
of the depression moved directly from Cork to Yarmouth, for 
the wind records prove that it passed north of Falmouth, and 
south of Holyhead and of Valentia. 
KEITH JOHNSTON, JUN. 

Perpetual Motion 
PROBABLY your sense of justice will induce you to insert some 
very brief remarks on your review of my article in the Quarterly 
Sournal of Science. The tone of the review is a penalty which 
all who venture to impugn commonly accepted theories must be 
prepared to submit to. Heresy in science meets with as little 
mercy as heresy in theology. I confess that in one sense of the 
word I am consciously a perpetual-motionist, but not in the sense 
of believing that any merely mechanical contrivance can produce 
— 
