464. 
to conceive how a recoiling atom of mass 14 or 16 
can produce an ionisation track of 4 cm. length in a 
mixture of helium and water vapour, after suffering 
a collision with an a-particle from polonium. The 
distance at which the collision took place was about 
3 cm. from the source. Probably the phenomena 
observed can best be explained on the assumption 
that here we have the case of the breaking up of a 
nitrogen nucleus by an a-particle with the expulsion 
of a hydrogen nucleus, which produces the long 
ionisation path. The cause of the large initial curva- 
ture of the path remains to be explained. It is not 
due to the superposition of a number of large-angled 
single scatterings. 
Further experiments are in progress. 
D. M. Bose. 
S. K. Guosu. 
University College of Science, Calcutta, 
February 21. 


Porto Santo in Pleistocene Times. 
THE Geological Society of America has recently 
published an extremely interesting review and 
summary of the recent work and opinions of specialists 
on the Pleistocene, by Dr. H. F. Osborn and Dr. 
C. A. Reeds. The chronology and changes of level 
are fully discussed, and we are invited to consider the 
evidence in favour of changes in sea-level depending 
upon the amount of water withdrawn as ice. It is 
improbable that the views of Depéret, in particular, 
will be accepted as they stand; but it must be 
admitted that the glacial periods produced some 
world-wide changes of level, and the question how | 
great these were becomes an extremely interesting one. 
The statement of these views is an invitation to 
geologists all over the world to search their coasts 
anew, and try to detect evidence of the postulated 
phenomena. In the course of this search I believe 
few places will better repay study than Porto Santo, 
in the Madeira group. I have on more than one 
occasion directed attention to the small I. de Cima, 
separated from the main island by a narrow and 
shallow channel (Boqueirao de Cima), yet possessing 
a very distinct species of snail in great abundance, 
found nowhere else. The postulated fall of the sea in 
glacial times would, I think, certainly unite Cima with 
the main island, yet the snail has not passed. That 
the snail has evolved in post-glacial times seems 
improbable. Between Cima and the main island 
are some rocks, and on one of these (Sircada) Miss 
Nancy Paterson collected for me some fossil snails, 
Ochthephila obtecta and others. I thought at first that 
we had evidence of a submerged island or neck of | 
land between Porto Santo and Cima, once supporting 
a snail-fauna, but now washed by the waves. Further 
investigation, however, convinced me that the Sircada 
Rock was nothing more than a large piece of the 
adjacent high cliff of the main island, which had 
fallen into the sea, carrying the fossils with it. 
Objection may be made that in postulating long 
constancy of level for the islets Cima and Baixo 
I do not take into account denudation, which would 
have worn them down had they not risen (or the sea 
fallen). These islets are essentially flat on the top, 
and wear away extremely slowly above, but rapidly 
along the sides, so that we have what may be called 
lateral denudation. This can be seen going on at the 
present time. 
Continuing the investigation, we naturally ask for 
marine pleistocene beds. These are to be found at 
the Campo do Baixo, west of the Villa Baleira on the 
main island. A wide well has been dug at this place, 
and it is possible to go down and explore it fully. At 
NO. 2788, voL. 111] 
NATURE 

[APRIL 7, 1923} 
a depth of about 30 feet is a layer of marine pleistocene 
rock, full of shells firmly cemented together. This 
rests on dense, dark, volcanic rock, but there is no 
evidence of volcanic activity in the material above. 
Far above the marine bed, near the surface, is dense 
sandy rock containing snail shells, Plebecula bow- 
ditchiana (Fér.), Ochthephila igctiformis (Sby.), ete. 
P. bowditchiana is an extinct species, but it is not 
certain that it lived so much later than the marine 
beds, for it might have been carried in shifting sand, 
though it is a heavy shell to travel in that manner. 
Another species of snail, Ochthephila coronata (Desh.), 
was found in the marine layer itself. A fine slab of 
the marine deposit, carrying many shells, has been 
presented to the British Museum. I broke up a 
quantity of the material, and submitted a series of 
the shells to Mr. J. R. le B. Tomlin, who has very 
kindly determined them as follows: Evato prayen- — 
sis Rochebrune, Mitra fusca Swainson, Cevithium 
vulgatum Brug., Bittiwm latreillei Payr. (abundant), 
Alectrion incrassata Mill., Trivia pulex Sol., Rissoa 
costulata Ald., Alvania teste Ar. and Magg., A. 
punctura Mont.(?), Mangilia striolata Sc., Natica 
sp. (? macilenta Phil., or perhaps sanctz-helene Smith), 
Anadema celatum A. Ad. (?), Calliostoma exasperatum 
Penn., Cardium papillosum Poli, C. tuberculatum L., 
Ervilia castanea Mont., Macrocallista chione L. To 
these I may add the common Columbella rustica L.. 
which was not submitted to Mr. Tomlin. A peculiar 
Naticoid and some others were not determined. — 
This is a modern fauna, many of the species still 
abundant in the sea near by. The place is not far 
from the sea, a short distance behind the line of sand 
hills, which are planted with tamarisk. The level of 
the deposit is little if at all below that of the shore, 
and we are not obliged to postulate anything more 
than a deeper bay, now largely filled up with sand. 
This brief discussion merely opens up the subject, 
and it is to be hoped that some student will pursue 
the matter further, combining a charming holiday 
with profitable research. T. D. A. CoCKERELL. 
University of Colorado, 
Boulder, 
February 21, 

The Hermit-Crab and the Anemone. 
In NATURE of December 2 and 30, 1922, vol. IIo 
(pp. 735 and 877), there are two very interesting 
letters from Dr. J. H. Orton on the relationship 
between these animals and the advantages of the 
partnership. Many years ag® (September igor) I 
took the opportunity, after a short visit to Millport, 
to watch the habits of the species Eupagurus prideauxit 
and Adamsia palliata, which seem always to live 
together, the association presumably being needful 
for their mutual welfare. Possibly my observations 
of these may be helpful in understanding the ways of 
other Paguride. 
On the occasion referred to, I brought with me 
to Sheffield a specimen of the hermit-crab and 
Adamsia living together. To ensure their being 
undisturbed during my experiments, they were 
settled by themselves in a small aquarium and 
regularly fed with oysters and cockles. I thus 
managed to keep them alive and healthy for nearly 
six weeks. The Adamsia, as is usual, had attached 
itself head downwards on the underside of the shell 
occupied by the hermit-crab, and the two sides of its 
base had grown upwards and round the shell, so as to 
meet in the centre above the back of the crab, forming 
a tube or sack for its accommodation, the crab having 
far outgrown the small Natica-shell, which, later, was 
found at the bottom of the sack. 

