bybe@ubuntu:~$ tar -tzf test.gz > /dev/null
bybe@ubuntu:~$ tar -tzf sitemapCP38.xml.gz > /dev/null
tar: This does not look like a tar archive
tar: Skipping to next header
tar: Exiting with failure status due to previous errors

bybe@ubuntu:~$ gunzip -c sitemapCP38.xml.gz | tar t > /dev/null
tar: This does not look like a tar archive
tar: Skipping to next header
tar: Exiting with failure status due to previous errors