ABSTRACTS OF LECTURES.
October 25th, 1894.
" THE GEOLOGY AND PHYSICAL GEOGRAPHY
OF CENTRAL AFRICA."
By the Senior Vice-President of the
Society, the Rev. E. MAULE COLE M.A., F.G S.
In his introductory remarks the lecturer said it was
a mistake to suppose that the geography of Central
was entirely unknown to the ancients. As a matter of fact the existence of
several 0fthe great Central lakes was known, and their position was set down
with some amount of precision by both Herodotus and Ptolomy. Ancient maps
circa 150 A.D., show the Nile issuing from two lakes and Portuguese maps of
the 15 Century also show some of the lakes ; but maps of
made at the beginning of the present century are quite blank in the vast
Dealing with Central Africa as now re-discovered by
Livingstone, Stanley, and Cameron, the lecturer said that the great
water-parting of the area was so situated that a single rainstorm might flow
in three directions -- by the Nile, northwards; by the Congo, westwards ;
and to the East, by the Zambesi. The great lakes of
Central Africa, like all lakes, are being filled up rapidly by
the detritus brought down by their tributary streams. The waters of the Victoria Nyanza are found to dry up at the rate of three
inches per year. The South end of this lake is a gentle slope, covered with
mud flats, and saline deposits, extending for thirty miles, showing the
previous extent of the waters. All round the Albert Edward Nyanza are
similar deposits. Lake Tanganyika occupies the western side of a great
hollow, 600 miles by 300 in breadth. The lake itself, 400 miles long by 20
wide, lies along a line of great disturbance. At one point, near the middle
of the western shore of the lake, there is a V shaped gap in the mountain
barrier. At this point Stanley
found a river running into the lake, but when Cameron visited the place he
found the water of the lake had risen so as to be level with the depression
and forming a morass. Subsequently Hore found a stream four feet deep
running violently out of the lake. In 1888 the lake had fallen 18 feet, but
the water was still running out of the depression, and the barrier of
detritus was cleared out down to the solid rock. Thus in quite modern times
the rainfall has overcome the evaporation and filled the lake up to the
brim. The water of Lake Tanganyika is fresh, but
Rukwa in the same district
is salt, and the water has now shrunk 40 miles from the old margin.
With regard to the volcanoes of
Central Africa, the lecturer said that the only knowledge we
possessed was that gleaned from the casual reports of travellers who were
not geologists. Between the Albert and
Lakes, was Mount Gordon
Bennett, in the crater of which live a people almost white. Many other
extinct craters had been found, in some of which there were crater lakes.
December 20th, 1894.
THE ENGLISH LAKE DISTRICT.
A. HARKER, M.A., F.G.S., (Cambridge
Mr. Harker began by describing briefly the oldest
rocks of the district, the Skiddaw Slates, which occupy a large area,
especially in the Northern part. In these rocks four or five fossiliferous
zones have been recognised of ages ranging from Tremadoc through Arenig to
Llandeilo. Owing to the great disturbance, the stratigraphical relations are
rather obscure, but it seems probable that all these fossils belong to the
Upper part of the Skiddaw Slates, which may therefore possibly include the
equivalents of zones lower in the Cambrian, not yet identified in the North
of England. Clifton Ward estimated the total thickness at 10,000 to 12,000
feet, but in view of the folding and faulting of the Strata, we cannot yet
attach much weight to such measurements.
Succeeding the Skiddaw Slates is the great succession
of volcanic rocks sometimes named the Borrowdale Series, constituting the
Central part of the district and forming most of the higher mountains. These
rocks were probably formed under water, and some of the tufts or ashes are
well banded; but, except near the top of the series, there is no admixture
of detritus with the volcanic material. The intercalated fossiliferous
sediments seen in the partly contemporaneous volcanic series of
are here wanting. Any decisive evidence regarding the exact sites of actual
volcanic centres is also yet to be obtained. The succession is a varied one.
So far as it is yet deciphered, the earliest rocks seem to be, as in
numerous other volcanic districts, lavas of intermediate composition which
we may term andesites. To these succeed basic lavas (basalts without
olivine) covering considerable tracts of country. Next comes a thick group
of fragmental accumulations (tufts and breccias), well seen in some of the
main mountain-groups such as those of Sea Fell, Bow Fell, and Helvellyn.
Finally we have acid rocks, chiefly lavas (rhyolites), and the upper flows
of these are interbedded with the succeeding Coniston Limestone.
The exact correlation of the Coniston
Limestone has been discussed by Mr. Mart, who has shown that it is divisible
into at least four distinct groups, each of which has its distinctive fauna
and its equivalents in other areas. There is not in this district, as in
some others, a stratigraphical break between the Ordovician (Lower Silurian
of the Geological Survey) and the Silurian proper. The lowest division of
the latter, the Stockdale Shales, equivalent to the Llandovery and Tarannon
beds of Wales, is an example of the extremely detailed subdivision which can
be introduced by means of careful paleontological study. Using chiefly the
characteristic species of graptolites, Mr. Marr and Prof. Nicholson have
recognised some fourteen distinct zones, some not more than a few inches
thick but still persistent over a large area, and corresponding with zones
containing the same fossils in the South of Scotland and in
Sweden. Of the succeeding groups, the
Coniston Flags, Coniston Grits and Bannisdale Slates correspond with the
Wenlock and lower Ludlow
of the Welsh Border, while the Kirkby Moor Flags are the equivalent of the Upper Ludlow.
The lecturer described the nature of the
remarkable system of crust-movements which followed the Silurian in this
district, the effects of which are seen in the folding and over-thrust
faulting of the Lower Palaeozoic rocks and
a great unconformity representing roughly the missing Old Red Sandstone
Strata. The Carboniferous and New Red rocks which border the district were
only briefly referred to. In Mesozoic times the area was elevated, probably
by slow degrees, into a dome-like form, and the result of this is still seen
in the radiate drainage system of the district; a system which was initiated
in consequence of this dome, but, by the gradual stripping off of the
Carboniferous and newer rocks, became superposed upon the Lower Palaeozoic
core of the district to which i has no direct relation.
The circumstances attending the
glaciation of the district and the origin of the lakes, which are now its
most striking feature, were only briefly touched upon in the concluding part
of the lecture.
January 17th, 1895.
PHOTOGRAPHY AS A MEANS TO THE STUDY OF
J. E. Bedford ESQ., F.G.S.
In his introductory remarks Mr. Bedford alluded to
the great advantage photography placed in the hands of the modern astronomer
and geologist, and in geology especially with regard to sections on the
coast and elsewhere which were constantly changing their aspect. The
lecturer however said he had not come to give an elaborate paper on the
subject but simply to show the Hull Society what had already been
practically accomplished by a few West Riding geologists in the direction of
geological photography. He then caused to be put on the screen a fine series
of views illustrating a wide range of formations throughout the
British Islands, including the Giant s Causeway, Fingal's
Cave, Port Erin, Snowdon, Llanberis, Bournemouth, the Cornish Coast,
Dunkeld, Arbroath, Skye, Malham, Dove Dale, Chee Tor, Flamborough, Filey,
"LIFE IN TIME" March 4th, 1895.
E. BOARDMAN, ESQ.
The lecturer first alluded to the immense thickness
of the stratified rocks, estimated by Lyell at 100,000 feet, and taking the
opinion of some geologists of the older school that the rate of deposition
might average one foot in one thousand years, made the age of the oldest
stratified rocks one hundred million years. Mr. Boardman then discussed the
evidence we have as to change in climate in the geological past, and the
various alleged causes of the same.
Finally the lecturer reviewed the paleontological
evidence as to the first appearance and development of organic Life on the
Earth --shewing that the fossil forms in the strata from Palaeozoic times
till now indicated a gradual passage from lower to higher forms of Life.
Copyright Hull Geological