Averaging Every Two Cells

I have some half-hourly data that I need to average into an hourly number. On the day change there is an annoying gap of two rows. Is there a formula/macro that could help me to ignore the gaps and average the half hour data into it's relevant hourly average number? Thanks in advance!

Example data:

02/01/2012 16h30 - 17h00 29.93
02/01/2012 17h00 - 17h30 39.89
02/01/2012 17h30 - 18h00 39.89
02/01/2012 18h00 - 18h30 62.23
02/01/2012 18h30 - 19h00 62.03
02/01/2012 19h00 - 19h30 59.79
02/01/2012 19h30 - 20h00 60.53
02/01/2012 20h00 - 20h30 57.92
02/01/2012 20h30 - 21h00 50.69
02/01/2012 21h00 - 21h30 48.46
02/01/2012 21h30 - 22h00 37.92
02/01/2012 22h00 - 22h30 30.92
02/01/2012 22h30 - 23h00 30.92
02/01/2012 23h00 - 23h30 57.23
02/01/2012 23h30 - 24h00 29.49
Données validées le 04/01/2012.

03/01/2012 00h00 - 00h30 24.77
03/01/2012 00h30 - 01h00 43.52
03/01/2012 01h00 - 01h30 22.35
03/01/2012 01h30 - 02h00 22.35
03/01/2012 02h00 - 02h30 14.91
03/01/2012 02h30 - 03h00 14.91
03/01/2012 03h00 - 03h30 10.27
03/01/2012 03h30 - 04h00 10.27
03/01/2012 04h00 - 04h30 9.99
03/01/2012 04h30 - 05h00 9.99
03/01/2012 05h00 - 05h30 16.88
03/01/2012 05h30 - 06h00 16.88
03/01/2012 06h00 - 06h30 34.89

Many thanks Marcol, that was very helpful! After using your code, to remove the resultant gaps i sorted the prices by size and then deleted the rows i didn't want, returning the sort to it's previous state after this.

thanks again for your help