﻿Related 
  Sedimentary 
  Surface 
  Forms. 
  191 
  

  

  apices 
  on 
  alternate 
  sides 
  of 
  each 
  ridge. 
  The 
  rectangular 
  

   type 
  consists 
  of 
  two 
  sets 
  of 
  ridges 
  intersecting 
  at 
  right 
  

   angles. 
  51 
  

  

  Figure 
  6 
  shows 
  a 
  plaster 
  cast 
  of 
  a 
  small 
  unlabeled 
  

   specimen 
  in 
  the 
  collection 
  of 
  the 
  Department 
  of 
  Geology 
  

   of 
  the 
  University 
  of 
  Cincinnati. 
  It 
  is 
  a 
  red, 
  thin, 
  hard, 
  

   sandy 
  shale 
  which 
  I 
  suspect 
  to 
  belong 
  to 
  the 
  Newark 
  

   Series, 
  judging 
  from 
  other 
  labeled 
  slabs 
  found 
  in 
  the 
  

  

  Fig. 
  6. 
  

  

  Fig. 
  6. 
  Hexagonal 
  interference-ripples 
  superimposed 
  on 
  current-ripples. 
  

   Plaster 
  east 
  of 
  a 
  specimen 
  of 
  red 
  sandy 
  shale; 
  c 
  = 
  the 
  narrow 
  dark 
  shadow 
  

   of 
  the 
  steep 
  face 
  of 
  the 
  current-ripples. 
  (For 
  dimensions 
  see 
  text.) 
  

  

  same 
  case. 
  It 
  is 
  covered 
  with 
  a 
  delicate 
  pattern 
  of 
  

   hexagonal 
  interference 
  ripples 
  which, 
  however, 
  in 
  this 
  

   case, 
  are 
  clearly 
  superimposed 
  on 
  typical 
  current-rip- 
  

   ples. 
  52 
  In 
  this 
  case, 
  the 
  orientation 
  of 
  the 
  pattern 
  was 
  

  

  51 
  For 
  illustration 
  of 
  the 
  rectangular 
  type, 
  see 
  Kindle, 
  1917, 
  pi. 
  23, 
  fig. 
  C; 
  

   of 
  the 
  hexagonal 
  type, 
  see 
  fig. 
  8 
  of 
  this 
  paper. 
  

  

  52 
  The 
  dimensions 
  of 
  this 
  specimen 
  are 
  as 
  follows 
  : 
  

  

  wave-length 
  amplitude 
  — 
  

  

  a 
  

  

  current-ripples: 
  31 
  — 
  4-5 
  cm; 
  0-3 
  cm; 
  10 
  — 
  25; 
  

  

  oscillation 
  ripples: 
  2-1 
  — 
  3-0 
  cm; 
  <01cm; 
  21 
  — 
  30; 
  

  

  (i.e. 
  the 
  cross-bars). 
  

  

  