﻿26 
  //. 
  E. 
  Gregory 
  — 
  Gravels 
  at 
  Cuzco. 
  

  

  has 
  remained 
  in 
  place, 
  while 
  the 
  canalized 
  stream 
  has 
  entrenched 
  

   itself 
  in 
  the 
  sands 
  and 
  gravel 
  bordering 
  the 
  Cuzco 
  basin. 
  

  

  Ground 
  Water. 
  — 
  A 
  large 
  proportion 
  of 
  the 
  water 
  which 
  

   falls 
  on 
  the 
  surface 
  of 
  the 
  Cuzco 
  fan 
  is 
  rapidly 
  absorbed, 
  and 
  

   percolating 
  downward 
  through 
  the 
  porous 
  gravels 
  to 
  a 
  depth 
  

   of 
  100 
  to 
  400 
  feet, 
  emerges 
  as 
  springs 
  along 
  water 
  courses 
  and 
  

   on 
  the 
  periphery 
  of 
  the 
  fan. 
  Springs 
  are 
  numerous 
  in 
  the 
  

   lower 
  part 
  of 
  Cuzco, 
  and 
  many 
  open 
  wells 
  within 
  the 
  city 
  

   reveal 
  permanent 
  supplies 
  at 
  a 
  depth 
  of 
  fifteen 
  to 
  twenty-five 
  

   feet. 
  On 
  the 
  northeast 
  border 
  of 
  the 
  fan 
  the 
  direction 
  of 
  

   ground-water 
  flow 
  is 
  southwest, 
  following 
  the 
  rock 
  slope 
  

   beneath 
  a 
  thin 
  superficial 
  cover 
  ; 
  on 
  the 
  west 
  border, 
  where 
  

   similar 
  relations 
  exist, 
  the 
  flow 
  is 
  east. 
  The 
  high 
  content 
  of 
  

   lime 
  in 
  well 
  and 
  spring 
  waters 
  is 
  due 
  to 
  the 
  presence 
  of 
  tiny 
  

   fragments 
  of 
  limestone 
  widely 
  disseminated 
  through 
  the 
  gravels 
  

   in 
  quantities 
  sufficient 
  to 
  furnish 
  calcareous 
  cement 
  for 
  the 
  par- 
  

   tial 
  consolidation 
  of 
  portions 
  of 
  the 
  mass. 
  One 
  result 
  of 
  

   ground-water 
  action, 
  which 
  has 
  also 
  an 
  archaeological 
  bearing, 
  is 
  

   the 
  presence 
  of 
  numerous 
  small 
  caves 
  and 
  pockets 
  and 
  shelves 
  

   in 
  the 
  steeply 
  inclined 
  gravel 
  walls, 
  — 
  cavities 
  which 
  mark 
  the 
  

   position 
  of 
  ephemeral 
  seeps 
  and 
  areas 
  of 
  less 
  consolidated 
  

   material. 
  The 
  floor 
  of 
  these 
  caves 
  is 
  covered 
  with 
  stratified 
  

   sands 
  and 
  they 
  appear 
  to 
  have 
  been 
  used 
  extensively 
  as 
  

   sepulchres. 
  

  

  Landslides 
  and 
  creeps 
  resulting 
  from 
  the 
  action 
  of 
  ground 
  

   water 
  may 
  be 
  observed 
  at 
  numerous 
  places 
  along 
  the 
  ravines 
  

   which 
  trench 
  the 
  Cuzco 
  gravels, 
  where 
  the 
  conditions 
  for 
  their 
  

   formation 
  are 
  exceptionally 
  favorable. 
  The 
  alluvium 
  rests 
  on 
  

   steep 
  rock 
  surfaces, 
  coarse 
  gravels 
  overlie 
  lenses 
  of 
  fine 
  sand 
  

   and 
  adobe, 
  the 
  water 
  courses 
  follow 
  deep, 
  narrow 
  canyons, 
  cut 
  

   in 
  unconsolidated 
  deposits, 
  the 
  amount 
  of 
  ground 
  water 
  is 
  

   relatively 
  large, 
  and 
  markedly 
  fluctuating 
  in 
  response 
  to 
  peri- 
  

   odic 
  showers. 
  Following 
  an 
  ordinary 
  storm 
  accompanied 
  by 
  a 
  

   heavy 
  downpour, 
  the 
  writer 
  observed 
  six 
  small 
  slides 
  and 
  

   numerous 
  seeps 
  along 
  the 
  Chunchullomayo 
  in 
  positions 
  where 
  

   vertical, 
  dry 
  gravel 
  walls 
  had 
  been 
  noted 
  on 
  previous 
  days. 
  

   In 
  the 
  heavier 
  gravel 
  masses 
  trenched 
  by 
  gravel-walled 
  canyons 
  

   the 
  effect 
  of 
  slides 
  is 
  chiefly 
  to 
  give 
  the 
  valleys 
  an 
  unsymmetri- 
  

   cal 
  shape 
  with 
  the 
  steeper 
  wall 
  on 
  the 
  side 
  toward 
  which 
  

   ground 
  water 
  flows. 
  In 
  valleys 
  where 
  one 
  bank 
  is 
  gravel 
  and 
  

   the 
  other 
  gravel 
  underlaid 
  by 
  rock, 
  the 
  lack 
  of 
  symmetry 
  is 
  

   very 
  pronounced, 
  — 
  a 
  perpendicular 
  wall 
  of 
  gravel 
  facing 
  a 
  

   moderate 
  slope 
  of 
  gravel, 
  decomposed 
  rock 
  and 
  miscellaneous 
  

   slide 
  debris. 
  Slides, 
  mostly 
  of 
  small 
  or 
  of 
  moderate 
  dimen- 
  

   sions, 
  are 
  conspicuous 
  along 
  the 
  Sappi 
  and 
  the 
  Ayahuaycco 
  

   where 
  they 
  extend 
  to 
  the 
  stream 
  bed 
  or 
  remain 
  as 
  plasters 
  

   attached 
  to 
  the 
  walls. 
  The 
  southwest 
  bank 
  of 
  the 
  canyon 
  por 
  

   tion 
  of 
  the 
  latter 
  stream 
  is 
  aUnost 
  continuously 
  faced 
  with 
  

  

  