614  Geological  Society  : — 
Terrestrial  Magnetism  and  its  Causes.     Byl?.  A.  Black.     London  : 
Gall  &  Inglis.  1905.  Pp.  226. 
According  to  the  author's  views,  the  "electric  waves,  or  electric 
displacements  in  the  ether'' which  are  projected  from  the  sun, 
"  dash  against  the  surface  of  the  earth,  or  at  least  the  enveloping 
atmosphere,  and  thus  come  under  the  influence  of  the  earth's 
movements  "  (p.  15).     "An  electric  sheet  is  thus  wound  around  the 
earth  from  apex  to  apex  in  the  course  of  the  diurnal  rotation 
The  sheet  may  be  compared  to  a  great  series  of  electric  wires 
wound  around  the  earth  from  east  to  west.  It  is  suggested  that 
this  would  furnish  a  simple  explanation  of  the  magnetization  of  the 
earth  "(p.  20).  Having  quoted  the  above  extracts,  we  feel  that 
it  is  unnecessary  to  add  anythingfurther,  as  they  are  quite  sufficient 
to  enable  our  readers  to  form  an  idea  of  what  sort  of  book  it  is  that 
we  are  dealing  with. 
Physics.  By  Charles  Piboeg  Mann,  the  University  of  Chicago, 
and  George  Eansom  Twiss,  the  Central  High  School,  Cleveland. 
Chicago  :  Scott,  Foresman  &  Co.  1905.  Pp.  x  +  453. 
The  writing  of  a  thoroughly  satisfactory  elementary  book  on 
physics  is  by  no  means  an  easy  task,  and  the  authors  of  the 
present  volume  are  to  be  congratulated  on  having  achieved  a  very 
considerable  amount  of  success  in  this  difficult  undertaking.  The 
book  is  just  of  the  type  that  will  appeal  to  youthful  minds  :  it  is 
profusely  illustrated,  and  at  every  point  the  principle  under 
discussion  is  exemplified  by  reference  to  some  real  thing  which  is 
already  within  the  sphere  of  the  reader's  experience.  The  style  is 
easy,  and  the  mode  of  treatment  full  of  suggestion  and  likely  to 
stimulate  the  imagination  and  awaken  the  interest  of  the  young 
student.  The  summaries,  questions,  problems  and  suggestions  to 
students  at  the  ends  of  the  chapters  are  also  admirable  features  of 
the  book,  and  must  have  involved  a  good  deal  of  time  and  trouble 
in  their  preparation.  There  is  a  striking  absence  of  pedantry  and 
dogmatism  about  the  book.  We  have  noticed  but  few  misprints  or 
errors,  but  would  suggest  the  substitution  of  "  rate  of  change  of 
motion  "  for  "  change  of  motion  "  in  the  last  line  on  p.  47. 
LV.  Proceedings  of  Learned  Societies. 
GEOLOGICAL  SOCIETY. 
[Continued  from  p.  424.] 
January  24th,  1906.— J.  E.  Marr,  Sc.D.,  P.E.S.,  President, 
in  the  Chair. 
HPHE  following  communications  were  read  : — 
1.  *  On  the  Igneous  and  Associated  Sedimentary  Kocks  of  Llan- 
gynog  ( Carmarthenshire).'  By  T.  Crosbee  Cantrill,  B.Sc,  and 
Herbert  Henry  Thomas,  M.A.,  P.G.S. 
The    sedimentary    rocks    associated    with    the    various    igneous 
masses  comprise  the  following  : — 
