﻿20 
  

  

  H. 
  E. 
  Gregory 
  — 
  Gravels 
  at 
  Cuzco. 
  

  

  extent 
  ; 
  at 
  one 
  

  

  Fig. 
  5. 
  

  

  bowlders 
  of 
  various 
  sizes 
  between 
  which 
  finer 
  materials 
  have 
  

   been 
  irregularly 
  deposited. 
  The 
  sand 
  beds 
  consist 
  of 
  fine 
  well- 
  

   washed 
  quartz 
  grains 
  which 
  in 
  places 
  are 
  bound 
  together 
  by- 
  

   films 
  of 
  calcareous 
  mud. 
  Through 
  the 
  body 
  of 
  the 
  fan 
  the 
  

   sand 
  is 
  displayed 
  as 
  lenses 
  rarely 
  exceeding 
  2' 
  in 
  thickness, 
  

   and 
  usually 
  dying 
  out 
  laterally 
  within 
  a 
  distance 
  of 
  100'. 
  The 
  

   largest 
  bed 
  observed 
  is 
  six 
  feet 
  in 
  thickness 
  and 
  extends 
  for 
  

   about 
  225'. 
  Near 
  the 
  upper 
  surface 
  of 
  the 
  fan 
  the 
  sand 
  lenses 
  

   are 
  more 
  abundant 
  and 
  have 
  a 
  somewhat 
  wider 
  

   point 
  constituting 
  nearly 
  1/5 
  of 
  the 
  material 
  exposed. 
  

  

  At 
  the 
  outer 
  edge 
  of 
  the 
  fan 
  where 
  its 
  deposits 
  interleave 
  

   with 
  silts 
  and 
  calcareous 
  muds 
  of 
  an 
  ancient 
  water 
  body, 
  sands 
  

   and 
  adobe 
  assume 
  the 
  leading 
  role, 
  the 
  gravels 
  playing 
  a 
  minor 
  

   part. 
  There 
  is 
  here 
  also 
  a 
  much 
  more 
  frequent 
  alternation 
  of 
  

   beds 
  and 
  a 
  much 
  greater 
  change 
  in 
  short 
  horizontal 
  distances. 
  

   The 
  stratified 
  phases 
  of 
  the 
  Cuzco 
  gravels 
  

   slope 
  in 
  general 
  southward 
  at 
  various 
  degrees 
  

   of 
  inclination. 
  At 
  the 
  mouth 
  of 
  the 
  canyon 
  

   portion 
  of 
  the 
  Ayahuaycco 
  the 
  well-stratified 
  

   beds 
  of 
  sand 
  included 
  within 
  the 
  gravel 
  mass 
  

   dip 
  south 
  at 
  an 
  angle 
  of 
  3°-5°. 
  At 
  the 
  edge 
  

   of 
  the 
  bluffs 
  facing 
  the 
  city 
  and 
  on 
  the 
  slope 
  

   northwest 
  of 
  Santa 
  Ana 
  church 
  dips 
  of 
  

   8°-10° 
  south 
  were 
  measured, 
  while 
  the 
  strata 
  

   which 
  cap 
  the 
  deposits 
  along 
  the 
  Anta 
  road 
  

   are 
  practically 
  horizontal. 
  Cross-bedding 
  

   though 
  present 
  is 
  not 
  a 
  conspicuous 
  feature, 
  

   doubtless 
  being 
  obscured 
  by 
  the 
  prevailing 
  

   unstratified 
  condition 
  of 
  the 
  gravels, 
  but 
  

   cut 
  and 
  fill 
  channels 
  trending 
  in 
  various 
  

   directions 
  are 
  revealed 
  in 
  nearly 
  every 
  sec- 
  

   tion. 
  

  

  The 
  accompanying 
  sections 
  (sec. 
  I 
  and 
  figs. 
  3-9) 
  illustrate 
  the 
  

   structure 
  and 
  arrangement 
  of 
  beds 
  in 
  selected 
  portions 
  of 
  the 
  

   delta. 
  

  

  H 
  2 
  ' 
  H 
  

  

  Fig. 
  5. 
  Section 
  

   IV, 
  Detail 
  of 
  gravel 
  

   shown 
  in 
  section 
  III; 
  

   size 
  and 
  orientation 
  

   of 
  pebbles 
  drawn 
  to 
  

   scale. 
  

  

  Section 
  I. 
  Mouth 
  of 
  Ayahuaycco 
  Quebrada. 
  

   Dip 
  4° 
  south. 
  

  

  1. 
  Soil, 
  red-brown, 
  sandy, 
  with 
  bands 
  of 
  brown 
  adobe, 
  

  

  streaked 
  with 
  calcareous 
  bands 
  and 
  penetrated 
  by 
  

   root 
  tubes 
  _ 
  

  

  2. 
  Gravel, 
  composed 
  of 
  subangular 
  pebbles 
  1 
  to 
  6 
  inches 
  

  

  in 
  diameter, 
  of 
  brown 
  and 
  grey 
  sandstone, 
  rarely 
  

   limestone; 
  partially 
  cemented 
  by 
  calcareous 
  films. 
  

   Bottom 
  rests 
  unconformably 
  on 
  the 
  channeled 
  

   surface 
  of 
  No. 
  3 
  

  

  Feet 
  

  

  10 
  

  

  