80 

sun during the last two or three years. These tended to show 
that the absorbing atmosphere, termed the chromosphere, which 
he had proved to exist round the sun’s body, had gradually 
diminished in thickness since the last solar spot minimum in 
1867.—Mr. Boyd Dawkins, F.R.S., gave a short account of the 
examination of Offa’s Dyke made in the autumn by Col. Lane 
Fox and himself, The portion examined extended from Cher- 
bury in the south to the abrupt range of limestone hills to 
the north of Llanamynech. At Nantcribba Hall, near For- 
den, the dyke passes nearly due north between the road to 
Montgomery and the abrupt hoss of volcanic trap which looks at 
a short distance like a ruined castle, and which has been en- 
circled by a yery broad and deep moat. There can be no doubt 
but that this was a point of observation, and as it is but some 
twenty yards on the English side of the dyke, it was most probably 
one. of the permanent positions occupied by the English followers 
of the Mercian King. From this point the dyke gradually sweryes 
to the east from the road between Montgomery and Buttington, 
and makes directly over the low slopes of the hills, in some 
places being nearly ploughed down, and in others, and especially 
in the small valleys, being of considerable height and resembling 
a railway embankment, until it reaches the higher ground of 
Fron. ‘Thence it runs through Pentre and gradually approaches 
the road, and finally dies away in the alluvium of the Severn, 
nearly a quarter of a mile to the south of Buttington Church. 
The commanding camp to the south of this portion of the line is 
Gaer Digol, or the Beacon Ring, on the top of the Long Moun- 
ain. The morass, which in Offa’s time must have extended be- 
ween the main ditch and the Severn, prevented the necessity of 
any bank being made between Buttington and the Cefn. Where, 
howeyer, the open country demands a defence to the north of 
Cefn, an embankment makes straight for the Greenstone ridge 
of the Garreg, and is very plainly seen close to the farm-house of 
that name, near the Trewern Gate. Here we lost our clue, and 
it is very likely that the steep ridges of Moel y Golfa, and the 
marvellously strong camps of the Breiddan and Middleton Hills, 
formed a sufficiently strong barrier without any dyke being raised. 
We picked it up again, however, on the western or Welsh side 
of the Severn, {rom which it runs, as shown in the Ordnance map, 
due north to the four crosses, where it joins the Oswestry road, 
and where it is cut across by the new railway. There it makes 
straight for the fortified hill of Llanamynech, its line coinciding 
with the high road. On reaching the summit of Llanamynech 
it takes the western or Welsh side of the two large camps, and 
passes down into the valley to the south of Whitehaven, which 
was the limit of our expedition, The results of our examination 
are the direct proof that the dyke was made for military pur- 
poses, and that it took the line which was best adapted for re- 
pelling the incursions of the Welsh. Throughout the district 
which was examined the embankment faces Wales, and was 
therefore made to defénd the country within it from the Welsh. 
Dr. Wright’s view, therefore, that it was a mere geographical 
boundary to prevent the Welsh from stealing the cattle of the 
Mercians cannot be maintained, although it may perhaps receive 
some confirmation from the nursery legend of Taffy. The camps 
in the neighbourhood of the dyke are probably older than Offa’s 
time. The bronze spears found in Llanamynech imply that the 
camp is not later than the bronze age, while the Roman coins in 
that of the Breiddan point to its occupation by the Romans. 
November 1.—Reyv. William Gaskell, Vice-president. in the 
chair. Mr. William H. Johnson, Mr. Walter Morris, and Pro- 
fessor Balfour Stewart were elected ordinary members of the 
Society. Dr. Joule exhibited a series of curves obtained by Dr. 
Stewart from the self-recording instruments at the Kew Obserya- 
tory, showing a large amount of disturbance of the magnetic de- 
clination and horizontal force during the progress of the aurora 
of the 25th October. Healso showed a curve of the changes 
which took place in the magnetic dip as observed by himself at 
Broughton. The most remarkable variation occurred during the 
interval from 6" 15™ to 6" 23m G.M.T., when the dip increased 
from 69° 8' to 70° 30'—‘“t Notes on Glacier Moraines in Cum- 
berland and Westmoreland,” by Mr. Brockbank, F.G.S. “The 
author referred to the proceedings of the Geological Society of 
London for 1840—1, which contain notices of the evidences of 
glaciers having existed in Great Britain, by Professor Agassiz 
Dr. Buckland, and others, and which point out (1) “ Moraine- 
like Masses of Drift,” which occur near the junction of the Ea- 
mont and Lowther with the Eden, near Penrith ; (2) The 
“large and tory insulated piles of gravel in the valley of the 
Kent near Kendal, and the smaller moraines and their detritus, 

NATURE 


[Mov. 24, 1870 
which nearly fill the valley from thence to Morecambe Bay ;” 
(3) ‘* Similar mounds near Shap,” and (4) the ‘* Gravel mounds 
near Milnthorpe and thence to Lancaster.” Of these the author 
considered the Kentmere Group, near Kendal, as most nearly 
fulfilling the conditions required in true glacier moraines, and 
that in the other cases it admitted of doubt whether they were 
really due entirely to glacial action. The districts more particu- 
larly the subjects of the author’s notes are (1) the valleys of 
Eskdale and the Duddon (which were not visited by Dr. Buck- 
land, but in which he supposed moraines to exist, from the ap- 
pearances of the valleys as delineated in Fryer’s map of Cumber- 
and) ; (2) the valleys eastwards from Bowfell ; and (3) the dis- 
trict of Shap Fells. 


DIARY 
THURSDAY, NovemMBeEr 24. 
Lonpon InsTITUTION, at 7.30.—On the Precious Metals and their Distri- 
bution; Prof. Morris 
Roya Society, at 8,30.—Note on the Pendulum Observations in India: 
Col. J. T. Walker, F.R.S.—The Theory of Resonance: Hon. J. W. 
Strutt. 
Society oF ANTIQUARIES, at 8.30.—Romano-Celtic Sword exhibited by 
Lord Wharncliffe: Mr. A. W. Franks.—Wall Decorations of the Roman 
Period in Sectile Work, especially in Glass: Mr. A Nesbitt. 
SUNDAY, NovemsBer 27. 
Sanne: Lecture Socmty, at 3.30.—On he Antiquity of Man: Dr. Cob- 
0 
MONDAY, Novemser 28. 
Lonpon InsTITUTION, at 4.—On Chemical Action: Prof. Odling 
INSTITUTE OF ACTUARIES, at 7.—On Legislation in reference to Life In- 
surance and Life Insurance Companies: Mr. T. B. Sprague, M.A. 4 
TUESDAY, NovemBeEr 29. 
GEOGRAPHICAL SOCIETY, at 8.30. 
MANCHESTER LITERARY AND PHILOSOPHICAL SOCIETY, at 7. 
WEDNESDAY, NoveMBER 30. 
Society oF Arts, at 8.—On Peat and its Profitable Utilisation: Robert 
M. Alloway. : " 
THURSDAY, DECEMBER 1. 
CuemicaL Socrery, at 8.—On some Derivatives of Anthracene: Mr. 
W. H. Perkin. 
LINNEAN SOcIETY, at 8. 
Lonpon InstiTuTion, at 7.30.—On Gems and Precious Stones: Prof, 
Morris. 
Society OF ANTIQUARIES, at 8.30. 
TUESDAY, DECEMBER 6. 
AntHRopoLoGicaAL Soctety, at 8.—On the Races inhabiting the British 
Isles: Mr. A. L. Lewis —On Archaic Structures of Cornwall and Devon : 
i A L. Lewis.—On Forms of Ancient Interment in Antrim: Dr. Sinclair 
olden. . : 


CONTENTS Bice 
Tue CLAIMS OF SCIENCE. . . . oe eect ao: 3) 5 
Tue Sources oF PHospHatic MANureEs. By E. Ray LANKESTER 
SCUINTINIG WEAR BOOKS . | (si teihee’s iis os Sets tule en nee 
OGRE BOOK'SHEDR ce cites Sere te betas Sat me de een 
Lerrers TO THE Eprror :— 
The Difficulties of Natural Selection.—A. W. Bennerr, F.L.S. 
T. R. R. Stepsinc; S$. N. CARVALHO; D. SHARP . . 4 oNGs 
The Chromosphere.—Rey. S. J. Perry . . . . 1. 2 1. 67 
From London to Catania | Se ; ee eee 
The Spectrum of the Aurora.—H. R. Procrer =| 4s) See 68 
The November Meteors—Rev. S. J. Perry ........ 6 
SPAIN AND THE Ecurpse EXPEDITION . . ......4.4,.~. , 
THE CONSTRUCTION OF Heavy ARTILLERY. (Wath [dlustrations.) . 69 
INDTESS FSA.) ST. 
. . . . oe ieaw - wee . . .  . . . 73 
Musicat InTERvats. By W. Sportiswoope, F.R.S.. . . . . . 75 
On THE GREAT MOVEMENTS OF THE ATMOSPHERE. By ALEX. Bucuan 75 
SOGIETIES AND ACADEMIES (77. Ds sa. ecien eete wee) ee 
TARR Rielle le fo Cela et hela a nt cet 
- 6r 
» 
- 62 
s « Gs 
0 gs 
. « 70 
Sree 


Errata.—Page 28, second column, line xo, for “‘cumulus” read “ nim- 
ne ee 54, first column, line 25 from bottom, for ‘‘ Mr. Care” read 
T Ort = oor 
