﻿376 
  GEOLOGY 
  OP 
  THE 
  NUBIAN 
  DESERT. 
  [Aug. 
  1 
  897, 
  

  

  beds 
  of 
  the 
  Nubian 
  Sandstone 
  — 
  probably 
  along 
  the 
  axes 
  of 
  low 
  

   saddles 
  — 
  and 
  throwing 
  off 
  the 
  stratified 
  deposits 
  on 
  all 
  sides. 
  He 
  

   noticed 
  the 
  suggestion 
  that 
  possibly 
  there 
  were 
  two 
  divisions 
  of 
  the 
  

   Nubian 
  beds 
  — 
  namely, 
  the 
  conglomerates 
  and 
  varied 
  strata 
  in 
  the 
  

   lower 
  part, 
  and 
  the 
  more 
  solid 
  sandstones 
  in 
  the 
  upper 
  (from 
  which 
  

   the 
  building-stones 
  of 
  the 
  great 
  temples 
  had 
  been 
  derived) 
  ; 
  but 
  the 
  

   question 
  whether 
  all 
  these 
  deposits 
  were 
  merely 
  variations 
  of 
  one 
  

   great 
  lacustrine 
  (or 
  estuarine) 
  formation, 
  or 
  were 
  distinct 
  formations, 
  

   could 
  be 
  determined 
  only 
  by 
  a 
  detailed 
  survey. 
  Regarding 
  the 
  

   igneous 
  rocks 
  which 
  occur 
  as 
  dykes 
  traversing 
  the 
  old 
  rocks, 
  it 
  was 
  

   clear 
  that 
  they 
  belong 
  to 
  some 
  period 
  intermediate 
  between 
  the 
  

   Archaean 
  and 
  the 
  Cretaceous 
  — 
  possibly 
  Upper 
  Palaeozoic. 
  He 
  

   thought 
  that 
  when 
  the 
  waters 
  of 
  the 
  old 
  wells 
  became 
  saturated 
  

   with 
  salts, 
  the 
  best 
  plan 
  would 
  be 
  to 
  sink 
  new 
  wells 
  close 
  by 
  

   in 
  favourable 
  positions, 
  in 
  which 
  the 
  waters 
  would 
  probably 
  be 
  

   found 
  less 
  saline. 
  

  

  The 
  Rev. 
  J. 
  F. 
  Blake 
  thought 
  that 
  geologists 
  seemed 
  rather 
  too 
  

   ready 
  to 
  suppose 
  comparatively 
  recent 
  changes 
  of 
  climate 
  to 
  account 
  

   for 
  phenomena 
  which 
  they 
  could 
  not 
  otherwise 
  explain. 
  En 
  the 
  

   present 
  case 
  the 
  depressions 
  in 
  the 
  river-beds 
  called 
  ' 
  potholes 
  ' 
  are 
  

   thus 
  accounted 
  for. 
  In 
  Cutch, 
  however, 
  there 
  were 
  numerous 
  

   similar 
  depressions 
  filled 
  with 
  water 
  all 
  the 
  year 
  round, 
  while 
  the 
  

   remainder 
  of 
  the 
  stream-course 
  was 
  dry 
  sand, 
  and 
  yet 
  there 
  was 
  

   evidence 
  that 
  the 
  general 
  conditions 
  of 
  climate 
  had 
  been 
  constant 
  

   for 
  a 
  long 
  time. 
  It 
  was 
  possible, 
  therefore, 
  that 
  in 
  the 
  case 
  of 
  the 
  

   district 
  described 
  a 
  varying 
  intensity 
  of 
  rainfall, 
  or 
  the 
  diversion 
  of 
  

   the 
  water 
  falling 
  on 
  higher 
  reaches 
  of 
  the 
  streams 
  into 
  other 
  

   courses, 
  owing 
  to 
  physical 
  changes 
  beyond 
  the 
  district 
  in 
  question, 
  

   might 
  account 
  for 
  the 
  present 
  lack 
  of 
  water, 
  without 
  any 
  very 
  

   serious 
  alteration 
  of 
  the 
  climatic 
  conditions. 
  

  

  Prof. 
  Bonney 
  said 
  that 
  it 
  had 
  occurred 
  to 
  him 
  that 
  possibly 
  the 
  

   lower 
  conglomerate 
  mentioned 
  by 
  Capt. 
  Lyons 
  might 
  be 
  pre- 
  

   Cretaceous, 
  like 
  those 
  described 
  by 
  Prof. 
  Hull. 
  He 
  did 
  not 
  think 
  

   that 
  much 
  good 
  would 
  come 
  from 
  sinking 
  fresh 
  wells. 
  As 
  regards 
  

   the 
  origin 
  of 
  the 
  wadis 
  and 
  rounded 
  stones, 
  he 
  did 
  not 
  see 
  how 
  

   these 
  phenomena 
  could 
  possibly 
  be 
  explained 
  without 
  a 
  heavier 
  

   rainfall, 
  and 
  that 
  climate 
  had 
  changed 
  was 
  a 
  geological 
  common- 
  

   place. 
  He 
  thought 
  that 
  the 
  wells 
  were 
  in 
  detritus. 
  

  

  