No entry for system.log in /etc/newsyslog.conf
An answer was posted in this ServerFault question.

Configuration of system.log moved in 10.9 to /etc/asl.conf. It should have a section like:

# Rules for /var/log/system.log
&gt; system.log mode=0640 format=bsd rotate=seq compress file_max=5M all_max=50M
? [= Sender kernel] file system.log
? [&lt;= Level notice] file system.log
? [= Facility auth] [&lt;= Level info] file system.log
? [= Facility authpriv] [&lt;= Level info] file system.log


The line beginning with &gt; system.log is analogous to the old newsyslog.conf line.

After editing the file, do:

sudo killall -HUP syslogd


to make it reload the configuration file.