8 NATURE 
[Wov. 2, 1882 
cemented into a more compact rock. I care‘ully watched the 
habits of the two species most numerous on the ‘‘ flats,” and in 
no case did I observe a single individual browsing on the patches 
of living coral. In truth it was on the dead coral rock f rming 
the ‘‘flats” of these reefs that these two species of Holothuriz 
subsisted ; and it appeared to me that they selected those feeding- 
grounds where the attachment of molluscs, zoophytes, and stony 
algze had to some degree loosened the surface of the rock. 
The particular species, on which my observations were made 
to determine the amount of coral sand daily discharged, pos- 
sessed a bluish-black body, from 12 to 15 inches in length when 
undisturbed, and with a circle of 20 pelate tentacles around the 
mouth, Without going into all the details of my methods of in- 
vestigation, it will be sufficient to state that from three inde- 
pendent observations on this species of Holothuria I have placed 
the amount of coral sand daily voided by each individual at not 
less than two-fifths of a pound (avoirdupois). At this rate some 
fifteen or sixteen of these animals would discharge aton of sand 
fron their intestinal canals in the course of a year, which repre- 
sents about 18 cubic feet of the coral rock forming the ‘‘ flat ” 
on which these creatures live. In order to illustrate this point 
more clearly, I will assume that every rood of the surface of the 
“flat” supports some fifteen or sixteen Holothuriz, a number 
which errs rather on the side of deficiency than of excess. In 
the course of a year 18 cubic feet of coral rock will be removed 
in the form of sand from the surface of each rood, which is 
equal to the removal of 1-605th of a foot per annum, or 1 foot 
in about 600 years. 
Although this estimate can be only regarded as of a tentative 
character and as applicable to but one species of the Holothuriz, 
it nevertheless throws some light on what I may term the 
““ organic denudation ” of coral reefs, and it is not unreasonable 
to suppose that where a fringing reef is undergoing a very 
gradual up-heaval, the combined operation of the fish, the 
mollusc, the annelid, and the echinoderm, may prevent it from 
ever attaining an elevation above the level of the sea at high 
water. i. B. Guppy 
H.M.S. Lark, St. Christoval, Solomon I-lands, June 30 
Railway Geology—a Hint 
Ir must often have occurred to others as well as to myself 
when making a long journey hy rail, and being whirled along 
all too fast through section after section of the greatest interest 
to the eye that can see in them something more than mere rail- 
way ‘‘cuttings,” how valuable would be some handbook giving 
the geolozical features of the country traversed by the principal 
railway lines, and illustrated by clearly drawn maps and 
sections. 
To give an instance—I have occa.ion pretty often to travel by 
the South Western line from Waterloo Station to Exeter, a 
route along which my untrained eye can take note of a succes- 
sion of instructive pictures, in the course of a five hours’ journey 
—the recent gravels, &c., covered by pine wood in the neigh- 
bourhood of Woking, broken abruptly at Basingstoke station 
by a section of the chalk, to be succeeded from here onwards to 
Salisbury by undulating downs of the same formation, bare of 
trees, and but-sparsely inhabited ; next, at the Yeovil junction, 
a sandstone quarry, riddled by martin’s nests, presumably of 
oolitic age ; then, between Axmi.uster and Honiton the greyish 
blue of a cutting through the lias ; to be final y succeeded, as I 
approach the term of my journey, by the rich red earths and 
loams of the new red sandst ne. 
Any other line, for instance, the Great Western, whi-b runs 
pare rllel to that just instanced, would give equally varied pictures ; 
and a copiously illustrated handb 90k, with notes explanatory, 
but as brief as possible —not only of the ground immediately 
bordering the line of rail, but of the general features of the 
nei-hbouring country within tne range of the eye of the tra- 
vel'er, should surely, I venture to think, have a large circulation. 
Will no geologist—a member of tae Government Survey, for 
instance—undertak+ the task ? 15 Cokes 
New University Club, Oct ber 27 
[We noticed a Guide of this kind for American railways in 
vol. xix. p. 287, and then suzgested the utility of a similar hand- 
boo < for England.—ED.] 
Complementary Colours 
of the bluish-green waters of Alpine rivers. The waters of the 
| mena which had been already shown ? 
I HAVE often noticed the complementary purple on the foam | Omission of all mention of Dr. Priestley’s name? 
Lake of Geneva, and of the Rhone at Geneva, as is well known, 
are not bluish-green, but greenish-blue ; but there also I have 
noticed what to my eye is exactly the same tint of purple on the 
foam. JosErH JOHN MurPHY 
Old Forge, Dunmurry, co. Antrim, October 28 
Palzolithic River Gravels 
THE recent articles and reports in your columns on the subject 
of Paleolithic river gravels bring three poiuts strongly forward, 
viz. :— 
1. The greit number of ‘‘ flint implements” 
flakes” found in the river gravels. 
2. The presence in the same deposits of bones of recent and 
extinct Mammalia. 
3- The entire absence of the bones of man. 
Such being the uniform results of persevering researches ex 
tending now for more than twenty-four years, it is surely time 
to request anthropologists to give (I) some explanation of the 
remarkable absence of human remains in deposits containing so 
many objects considered to be of human manufacture, and (2) 
some proof that it is absolutely impossible for these so-called 
“*flint implements ’’ and ‘‘ flint flakes” to have been formed by 
natural causes. C, Evans 
Hampstead, October 18 
and ‘° flint 
LAVOISIER, PRIESTLEY, AND THE 
DISCOVERY OF OXYGEN 
] T is a matter of very little importance whether Lavoisier 
actually obtained oxygen gas a few weeks or days 
before Priesdey. The bare bald discovery of the gas is 
a very minor matter when placed in juxtaposition with 
the astounding revolution produced in chemistry by La- 
voisier ; with the admirable series of experiments, the 
acute reasoning, the elegant logical penetration, which 
enabled him to overthrow the theory of Phlogiston when 
literally all Europe supported it. The discovery of oxygen 
dims and pales before the development of the theory of 
combustion, the theories of acidification, of calcination, 
of respiration, and the introduction of exact quantitative 
processes and instruments of precision into chemistry. 
But it matters much whether the fair fame of one of the 
noblest and wisest men in the long roll of illustrious 
natural philosophers is to remain with a grievous slur cast 
upon it. It matters much whether his reputation is to be 
blasted by the reproach that he claimed the discovery of 
oxygen, knowing well that Priestley had preceded him. 
It is with a view of removing this slur upon the memory 
of the founder of modern chemistry, and certainly not 
with any thought of adding one iota to his long list of 
greater triumphs, that we have examined into the true 
bearings of the question. 
First as to the accusations. Dr. Thomas Thomson, in 
his “ History of Chemistry,’’ 2nd edit., 1830, vol. ii. p. 19, 
writes : ‘ Lavoisier, likewise, laid claim to the discovery 
of oxygen gas, but his claim is entitled to no attention 
whatever, as Dr. Priestley informs us that he prepared 
this gas in M. Lavoisier’s house in Paris, and showed 
him the method of procuring it in the year 1774, which is 
a considerable time before the date assigned by Lavoisier 
for his pretended discovery.’’ Again, p. 106: ‘‘ Yet in the 
whole of this paper the name of Dr. Priestley never occurs, 
nor is the Jeast hint given that he had already obtained 
oxygen gas by heating red oxide of mercury. So far from 
| it, that it is obviously the intention of the author of the 
paper to induce his readers to infer that he himself was 
the discoverer of oxygen gas. For after describing the 
process by which oxygen gas was obtained by him, he 
says nothing further remained but to determine its 
nature, and ‘I discovered with such surprise that it was 
not capable of combination with water by agitation,’ &c. 
Now why the expression of surprise in describing pheno- 
And why the 
1 con- 
fess that this seems to me capable of no other explanation 
