Unknown Calendar: where does it come from? Within Calendar (6.0) on Mountain Lion, beside my own 12 calendars, I noticed a calendar named Calendar.

I didn't create it. All my calendars are coming from a recent migration
from Snow Leopard to Mountain Lion.

Where does this Calendar come from?
Is this a default calendar automatically created by Calendar (the application)?

Through an export (under ics format) I discovered that it is empty.

I'd like to remove this abnormal Calendar. 
Does anyone know if this default calendar is necessary for one of the Calendar functions?
Looking at the directories:

~/Library/Calendars/*.calendar


where all calendars are stored, the command:

grep string ~/Library/Calendars/*.calendar


let me identify among the 4 strings found, which one of these directories
was the one containing my Calendar ghost calendar:

    [...]
    &lt;string&gt;#0E61B9FF&lt;/string&gt;
    &lt;string&gt;22228888-4444-6666-AFAF-AAFF00005555&lt;/string&gt;
    &lt;string&gt;Calendar&lt;/string&gt;
    &lt;string&gt;Local&lt;/string&gt;
    [...]


From the date of modification of directory:

% ls -l 22228888-4444-6666-AFAF-AAFF00005555.calendar
drwx------  4 hal  hal  170 Sep 21 17:10 22228888-4444-6666-AFAF-AAFF00005555.calendar
%


I diagnosed that this Calendar was imported through my first
synchronisation from a new iPhone containing just its default calendar
named Calendar.

Even with all my calendars more fresh on my Mac, this unexistent default
Calendar was imported.

I removed it on my Mac and made one more synchronisation to get rid of it on my iPhone and my Mac.