APRIL 7, 1904] 
NATURE 
549 
and Loch Benachally the town of Blairgowrie. The results 
obtained by the Lake Survey must be of particular interest 
to these municipalities, as indicating the capacities and the 
depths of the lochs from which they draw their water- 
supplies. Lochs Daimh, Kennard, Turret, and Fender, 
though small lochs, are interesting on account of their re- 
latively great depth. The little Loch Fender, which has 
an area of only some 22 acres, is especially striking in this 
respect. 
Temperature observations were made at the time of sound- 
ing most of the lochs, and the results are given under each 
loch. In the case of Loch Rannoch, the observations ex- 
tended over a period of four months, and gave some interest- 
ing results as to the march of temperature throughout the 
waters of the loch from March to July, 1902, but usually 
the observations are too few to afford material for dis- 
cussion, though they are available for comparison with any 
future observations. 
The bathymetrical maps illustrating the papers are a 
distinctive feature, and are excellent examples of chromo- 
lithographic work. They are reduced from the Ordnance 
Survey charts to the uniform scale of 3 inches to the mile. 
The water-surfaces are tinted in deepening shades of blue, 
the darkest shades indicating the greatest depths. The 
land-surfaces are tinted in deepening shades of brown, the 
darkest shades indicating the highest elevations. Longi- 
tudinal and cross sections of the principal lochs are given, 
the true vertical relief drawn to scale being shown in solid 
black, while coloured extensions in outline represent the 
vertical scale exaggerated five times in order to show the 
relative depth with greater effect. Besides the maps there 
are numerous woodcuts in the text, some of which are repro- 
duced in this notice. 
Appended to the concluding paper are some valuable notes 
on the geology of the Tay basin, by Drs. Peach and Horne, 
illustrated by an admirable geological map, and on the 
biology of the lochs of the Tay basin, by Mr. James Murray, 
assistant zoologist on the staff of the Lake Survey. 
In their concise sketch of the geology and glaciation of 
the district, Drs. Peach and Horne show that the Tay basin 
is geologically divided into two parts by the great fault 
along the Highland border—to the north-west metamorphic 
rocks pierced by igneous intrusions, to the south-east rocks 
of Old Red Sandstone age with a small patch of Carbon- 
iferous strata. Most of the lochs lie to the north-west of 
the Highland fault, and the groups of strata are enumerated 
in the order in which they are met with on proceeding 
northwards from the fault, their distribution being in- 
dicated, and the system of north-east and south-west dis- 
locations which traverse the metamorphic area discussed. 
After dealing with the lower and upper divisions of the Old 
Red Sandstone, which occur to the south-east of the border 
fault, the authors proceed to consider the evidence relating 
to the glaciation of the Tay basin, which leads to the con- 
clusion that, during the climax of the Ice age, the region 
must have been covered with one continuous sheet of ice; 
striz have been found up to elevations of 3000 feet, show- 
ing that the highest mountains were over-ridden by the ice, 
the movement of which must to some extent have been in- 
dependent of the existing valley-system. This stage was 
followed by a period of confluent glaciers, when the ice 
streamed over passes connecting adjoining valleys, leaving 
in its track lines of moraines. Finally, there was the phase 
of corrie-glaciers, when the glacial detritus was borne for 
no great distance from the local centres of dispersion. 
The majority of the lochs within the Tay basin, most of 
them small and comparatively shallow, lie in the midst of 
drift deposits ; several other lochs, some of considerable size, 
lie along lines of displacement, for example, Lochs Ericht, 
Garry, Laidon, and Lyon, the long axes of which coincide 
with the courses of more or less powerful dislocations. As 
typical examples of rock-basins eroded by ice-action, Lochs 
Rannoch, Tummel, Earn, Iubhair and Dochart are cited. 
The two last-mentioned originally formed one sheet of 
water, and have been separated by alluvial material brought 
down by the river; Loch Dochart is being rapidly silted up, 
and must formerly have extended three miles up the valley. 
Further up Glen Dochart a strip of alluvium five miles in 
length may probably represent a silted-up rock-basin. 
Tay presents certain features differentiating it from the 
rock-basins cited, there being no rocky barrier close to the 
NO. 1797, VOL. 69] 
lake, and the Loch Tay fault runs along the course of the 
lake for a distance of 53 miles, the deepest part of the basin 
coinciding with this fault, to which the deflection of the 
original valley of the Tay must be due. Thus Loch Tay 
cannot be regarded as a typical example of a rock-basin, 
but the other rock-basins referred to seem to furnish strong 
evidence in support of the theory of ice-erosion. 
Tow-net collections were taken in most of the lochs in 
the Tay basin, and have furnished Mr. Murray with material 
for some interesting notes on the plankton of the open 
water of the different lochs. The number of species is not 
very great, and does not vary much; each loch has a distinct 
character, which, notwithstanding a considerable amount 
of seasonal variation, is pretty constant. The genera and 
species usually met with in the open water of the lakes are 
enumerated, and although all the forms may be present in 
most of the lakes, the varying proportions in which they 
occur give rise to great differences in the character of the 
plankton. This lacustrine type of plankton was found even 
in the smallest lochs surveyed. Some of the forms are sub- 
ject to considerable variation, and sometimes a single 
organism, usually vegetable, will so increase in a loch as 
to form a ‘** Wasserblut.’’ A brief account of the plankton- 
organisms observed in some fifty of the lochs visited is 
given. 
THE HOPE REPORTS. 
HE fourth volume of the ‘‘ Hope Reports’”’ contains 
twenty papers bearing upon the study of insects in 
particular and the theory of natural selection in general. 
The most important of these is Mr. Shelford’s paper on 
mimetic insects and spiders from Borneo and Singapore. 
So long as we had only a few isolated cases of mimetic 
resemblance between animals belonging to different families 
or orders, it was possible for the opponents of the theory of 
natural selection to make light of them or to urge with 
some force the argument of the influence of similar external 
conditions, but as the number increases the difficulty of 
accounting for these wonderful mimetic resemblances by 
any other theory than that of natural selection becomes in- 
surmountable. Mr. Shelford’s list of mimics and their 
models is a long one, and as his description is accompanied 
by valuable field notes and is illustrated by five excellent 
coloured plates, it forms one of the most important contri- 
butions to the literature of the subject which has yet been 
published. The figures were drawn from the dried speci- 
miens as they arrived in this country, and in some cases the 
mimicry does not seem to be a very close one as it may be 
judged by the illustrations only, but it is in these cases that 
the value of the field notes lies. 
In the description of a fly belonging to the genus Sepedon 
that mimics a hymenopteran (Collyris emarginata, Macl.), 
Mr. Shelford says :— 
‘““ Both of the species now under discussion were caught 
together on the wing on Mt. Serambu, Sarawak, and when 
seen alive and actively moving about were not readily dis- 
tinguishable. As cabinet specimens they furnish an instance 
of the importance of field-work in the study of mimicry, and 
of the unreliability of dead impaled insects or mere figures 
unless, indeed, both are prepared with reference to careful 
observations of the living forms. The fly when alive was 
of a very brilliant blue like that of the Collyris, but the 
colour has now faded to a dusky indigo, while the abdomen 
being much shrunk detracts considerably from the previous 
resemblance. The legs are brilliant red, and constituted 
one of the most conspicuous features of both fly and beetle.”’ 
The tables that Mr. Shelford gives of the arrangement of 
these insects which mimic and are mimicked into convergent 
groups should be carefully studied by naturalists who may 
have the opportunity to study insects in the tropics. 
An important series of experiments on the colour relation 
between lepidopterous larva and their surroundings is de- 
scribed by Prof. Poulton. In Gastropacha quercifolia the 
susceptibility to the colour surroundings appears to be re- 
stricted to the younger stages of the larva, but in further 
experiments Prof. Poulton found that in Amphidasis betu- 
Loch | laria every stage except the first and the fifth or sixth is 
1 “The Hope Reports.” (Printed for Private 
Circulation.) 
Vol. iv., 1900-1903. 
