May 27, 1886] 
NATORE 
81 
twinned felspar microliths has formed round them. 
These bodies lie approximately normal to the surface of 
the residual kernel, which they actually penetrate like 
pins set in a cushion. Zoisite also, which is present in 
nearly all the altered sandstones, as a product of meta- 
morphism, sometimes pierces the quartz from outside. 
Augite and hornblende have likewise been developed, 
not infrequently as microliths, which, though grouped 
together in one common crystallographic outline, are not 
united. 
Further stages of change are described as occurring in 
certain rocks where the fragmental character, though to the 
unaided eye still traceable, is found to have been replaced 
by an entirely crystalline structure, giving rise to rocks 
which must be classed with the diabases. These masses 
sometimes have their pyroxene in the form of diallage, 
and are destitute of olivine, but usually contain much 
zoisite and frequently also hornblende. Diorites of similar 
origin occur, sometimes with a predominance of horn- 
blende as in true amphibolites. 
The shales are silicified and intersected by innumerable 
quartz-veins, in which, or projecting from their walls, are 
frequently abundant zoisite crystals. Yet the meta- 
morphism has not destroyed the microscopic fossils con- 
tained in the strata. But the most remarkable example 
of metamorphism cited by Mr. Becker is the conversion 
of these same felspathic sandstones into serpentine—an 
alteration referred to in Prof. Whitney’s description of 
this region. He asserts that field observation con- 
clusively proves the great mass of the serpentine, 
estimated altogether at more than 1000 square miles, to 
have been made out of the sandstones, either immediately 
or through an intermediate granular rock. Sections are 
seen where sandstone shades off into serpentine, and 
areas of highly-inclined sandstones pass along the strike 
into the same rock. In this conversion, the change begins 
along the cracks, working toward the centres of the 
included fragments, and producing a structure like that 
seen in decomposing olivine. The felspar fragments are 
corroded externally, their cracks being irregularly widened 
and filled with serpentine which sometimes projects as 
teeth into the clear felspathic mass. Even the quartz- 
grains have not been able to resist the alteration, but may 
be seen with their outer parts replaced by serpentine, 
which likewise penetrates their interior in long slender 
green needles. 
pentine, and the same transformation may be surmised 
in the case of mica and garnet. Mr. Becker states that 
chemical analyses and microscopic tests demonstrated 
that the serpentine diffused through the sandstones and 
forming the massive exposures is all the same mineral. 
He will no doubt in due time produce the detailed evi- 
dence on which his statements are founded. In the 
meantime he will of course be prepared for much scepti- 
cism and even for angry denial of his results. The careful 
elucidation of the problem he has attacked cannot but be 
of enormous service in throwing light upon the vexed 
question of metamorphism. He claimsthat the rocks which 
he has been investigating furnish a colossal example of 
regional metamorphism of which all the successive stages 
can be studied. Many thousands of square miles of rock 
have been subjected to such intense lateral compression 
that they have been utterly shattered, the average size of 
the unbroken lumps not being greater than that of an egg. 
In rocks thus crushed warm interstitial water would have 
potent chemical reactions. Warm basic solutions are 
believed to have first been produced, and to have con- 
verted the sandstones and some of the shales into holo- 
crystalline compounds containing augite and hornblende. 
Serpentisation is supposed to have followed at a lower 
temperature, while silicification came last, as the solutions 
finally became acid. Geologists will await with im- 
patience the appearance of the monograph in which 
these conclusions are maintained. 
Apatite has also been replaced by ser- | 
THE COMPOSITION OF THE EDIBLE BIRD S- 
NEST (COLLOCALIA NIDIFICA) 
HE nature of the material which forms the edible 
bird’s-nest has been the subject of some controversy. 
In 1817 Sir Everard Horne (Phzl. Trans., 1817, p. 337) 
suggested that it is the product of the activity of certain 
glandular structures which he figures in his paper, and 
which he associates with the gastric glands. In the 
“Origin of Species” (6th ed., p. 228) Darwin indorses 
the view of its being entirely a secretion by the bird, 
speaking of it as ‘“‘inspissated saliva,” and showing how 
the amount of saliva devoted to nest construction differs 
with different species. He mentions in particular a 
North American species which he says “ makes its nest 
(as I have seen) of sticks agglutinated with saliva and 
even with flakes of this substance.” Writing at about the 
same time, Bernstein (fournal fiir Ornithologie, 1859, 
p- 111) connects the nature of the material with certain 
developments of the bird’s salivary glands, which he says 
are noticeable during the nest-building season. 
On the other hand, it has been maintained by many 
observers that the nest of this species of swift is con- 
Fig! 
Celebes nest. Lamellated structure (mag. 59 diam.). 
structed similarly to the North American species referred 
to by Darwin, the chief difference being that instead of 
sticks the bird uses certain alge which are found in con- 
siderable masses on the walls of the caves which they 
frequent in the breeding season. Other alge also have 
been suggested as those used. 
It has further been supposed that the alge are par- 
tially digested before being utilised, and that after re- 
gurgitation the material so acted on is worked up into the 
form of the nest. 
A suggestion was made by Mr. E. L. Layard, H.M. 
Consul in New Caledonia, in a letter to NATURE, Sep- 
tember 17, 1884 (p. 82), which seemed to reconcile the 
conflicting theories. He says that the first quality of 
nest which is produced early in the breeding season con- 
sists entirely of animal secretion, but that later on, if the 
first nests are destroyed, the birds cannot replace them 
by this secretion alone, and so use extraneous substances 
to help in the construction. The second and inferior 
qualities of nest are so formed differently from the first. 
In a paper published in the Fournal of Physiology 
(vol. vi. p. 40), | have given the results obtained from an 
