The file is an ordinary Windows/DOS text file.
Lines are delimited by a carriage-return/line-feed pair.
Fields (columns) are delimited by a tab character.
Fields are not further enclosed (no quotes around text fields, for example).
It appears that, in the mode in which I'm using the import facility,
the utility is expecting a Unix-style text file, in which fields are
delimited by a single character (line feed?).
Thanks.