PROCEEDINGS OE THE PERTHSHIRE SOCIETY OP NATURAL SCIENCE. 
267 
May 6th, 1886. 
R. D. Pullar, Esq., F.C.S., Vice-President, 
in the Chair. 
NEW MEMBER. 
Mr John Purves, Tullypowrie, Grandtully, was elected. 
DONATIONS. 
The following were announced :— 
One large swan, two young fox cubs, and one mountain 
hare—from Sir Robert Menzies, Bart.; two tawny owls— 
from Lady Helen Macgregor, Edinchip; and one black¬ 
bird, spotted with white—from Miss Wood, Freeland. 
EXHIBITIONS. 
Mr H. Coates exhibited the following 
1. A specimen of the horse-mussel (Mytilus modiolus), 
from the Firth of Forth, containing a pea-crab. This 
little crab is frequently found living within the shell of 
the live mussel, and formerly it was supposed to act as 
sentinel, and to warn its host of approaching danger. 
This zoological myth formed the subject of allusions both 
by Cicero and Pliny, and has also formed the theme of 
modern English poetry. The reason why the crustacean 
chooses such a habitat does not seem to be quite understood. 
2. A specimen of Mya truncata, a bivalve which lives 
buried in the mud, through which it extends a breathing 
tube. Attached to the shell was the horny covering which 
envelopes this breathing tube. 
The following papers were read :— 
1. “ The Life History of the Frog." By Mr James 
Stewart, L.D.S, 
2. “ The Ocean and its Currents .” By Mr R. Brown, 
C.E., R.N. 
The following is an abstract of part of Mr Brown’s 
paper:— 
The surface of the earth may be marked off into three 
great areas—First, the Continents, covering roughly five- 
sixteenth’s of the earth’s surface, and having an average 
height of 900 feet above the level of the sea. Second, an 
abysmal region, with water of not a less depth than 1500 
fathoms, covering 8-16ths, or one half of the earth’s surface, 
the average depth of which is three miles. There is a 
region between these two called a border or transitional 
region covering 3-16ths of the earth’s surface, and connect¬ 
ing the three great elevated plateaux of the Continents 
with the great submerged plain of the abysmal regions. 
In the border region deposits are now being laid down 
which are chiefly made up of the debris of the adjacent 
Continents—deposits resembling in almost all respects 
those out of which the sedimentary rocks making up the 
present Continents must have been formed in past ages. 
In the abysmal areas there are here and there small 
volcanic islands, rising as great cones from the bottom of 
the sea, sometimes capped with coral reefs, but there are 
in those areas no traces of Continental rocks; indeed, it is 
extremely unlikely that any Continental land ever existed 
in these abysmal regions during past ages, and the deposits 
now forming in them, far from the present Continental 
lands, have, so far as is known, no analogues in the 
geological series of rocks. While there is no evidence that 
Continents ever existed in the areas now composed by the 
abysmal regions, the ocean, on the other hand, has, in past 
times, flowed over nearly every portion of the Continents. 
What are now Continents have been broken up into islands 
of great or small size, and many islands, like Britain, 
Japan, the Phillipines, Australia, &c., at different periods 
of time formed parts of the existing neighbouring 
Continents. Wide seas have thus been formed over the 
land areas of past geologic times. Those seas, probably, 
never have had a depth nor an extent comparable with the 
depth and extent of the present great oceanic basins, but 
they have often had a depth of many hundreds of feet, and 
were frequently filled with pure oceanic waters. 
The breaking up of the land in this way has been among 
the chief factors in the distribution of climate in the past 
as well as at the present time; for by diverting equatorial 
oceanic currents, or by cutting them off from high latitudes, 
a given fauna or flora has been able to flourish in widely 
different latitudes on the surface of the earth. Of the five 
great areas into which the oceanic waters are usually 
divided by geographers, the Arctic and Antarctic Oceans 
are but little known, impassable barriers of ice having been 
met with wherever an attempt has been made to penetrate 
into them. Of the other three oceanic basins, the Atlantic, 
Pacific, and Indian Oceans, much real, accurate, useful, 
and important information has been acquired in late years. 
The length of the Atlantic basin, considered as extending 
