Vol.  49.] 
THE  RISE  AND  FALL  OF  LAKE  TAX G  AN  YIKA . 
579 
44.  The  Rise  ancl.  Fall  of  Lake  Tanganyika.  By  Dr.  Robert 
Sieger.  (Communicated  by  the  President.  Read  June  21st, 
1893.) 
Perhaps  I  may  be  permitted  to  offer  a  few  remarks  concerning 
Mr.  A.  Carson’s  interesting  paper,  published  in  vol.  xlviii.  of  this 
Journal,  p.  401.  That  author  regards  the  rise  and  fall  of  Lake 
Tanganyika  as  a  purely  local  phenomenon,  due  to  alterations  of 
its  outlet,  the  Lukuga,  which  was  blocked  up  a  long  time  ago,  but 
reopened  between  the  years  1874  and  1879  ;  and  he  discusses  in  a 
very  careful  manner  the  geological  conditions  necessary  for  the 
damming-up  and  the  outburst  of  the  lake.  Another  opinion,  now 
very  common  among  German  geographers  and  maintained  by  myself, 
treats  these  great  oscillations  of  the  level  of  Lake  Tanganyika  as 
analogous  to  the  variations  reported  of  other  African  lakes  and 
resulting  simply  from  climatic  changes.  I  believe  that  there  is  no 
absolute  contradiction  between  these  two  opinions,  and  that  it  is 
possible  to  arrive  at  a  satisfactory  explanation  of  the  phenomena 
in  question  by  combining  the  influences  of  climate  with  those  of 
mechanical  agencies. 
The  meteorological  explanation  of  lake-  and  river-variations  has 
been  given  already  in  a  very  important  paper  by  Prof.  H.  Fritz,  of 
Zurich,  published  in4  Petermann’s  Mittheilungen,’  vol.  xxvi.  (1880), 
pp.  245  et  seqq.  I  regret  that  I  was  not  aware  of  the  existence 
of  that  memoir  at  the  time  of  my  own  first  essays  on  the  variations 
of  level  in  African  and  other  lakes.  Prof.  Fritz  held  it  impossible 
that  the  amount  of  rainfall  should  vary  and  the  temperature  oscil¬ 
late  in  the  same  manner  over  the  wThole  surface  of  a  continent  or  of 
the  globe,  but  he  held  that  there  is  a  sort  of  compensation  between 
the  different  areas.  Subsequently,  Prof.  Bruckner,  now  of  Bern 
(chiefly  in  his  valuable  work  on  4  Elima-Sehwankungen,’  Vienna, 
1890),  and  myself,  succeeded  in  demonstrating  a  surprising  coinci¬ 
dence  of  the  epochs  of  oscillation  in  a  great  many  lakes,  rivers,  and 
glaciers.  This  can  hardly  be  explained  otherwise  than  by  general 
oscillations  of  climate,  indicated  by  meteorological  observations,  and 
proved  beyond  doubt  by  Prof.  Bruckner’ s  laborious  researches. 
In  the  course  of  my  study  of  the  secular  oscillations  of  lakes,  I 
published  two  short  papers  on  the  lakes  of  the  Dark  Continent, 
copies  of  which  I  have  now  sent  to  the  Geological  Society’s 
library.1 
I  have  found  that  the  culminating  points  of  cold-and-moist  periods 
stated  by  Prof.  Briickner  to  approximately  coincide  with  the  years 
1850  and  1880,  and  even  the  warm-and-dry  period  culminating  in 
1860,  also  coincide  with  the  dates  of  the  maxima  and  minima  of 
level  of  the  Central  African  lakes.  The  reader’s '  attention  is 
directed  in  this  connexion  to  the  great  floods  on  Lake  Tsad  at  the 
1  Jahresbericht  des  Vereines  der  Geograpben  an  der  Universitat  Wien 
voL  xiii.  (1887),  and  ‘  Globus,’  vol.  lxii.  no.  21,  Brunswick,  1892. 
