Revision History for USGS 
  Crustal Studies Technical Letter Number 18

  Robert Rodriguez, William P. Durbin, Jr., J.H. Healy, and 
  David H. Warren

  Compilation of Seismic-Refraction Crustal Data in the 
  Soviet Union

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  Posted online at http://pubs.usgs.gov/misc/tl/0018/
  August 8, 2012

  Initial release in paper form
  February 28, 1964

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