convert a lost+fouind partition to ext4

[Abhishek Dixit]

Hi on  my disk
 sudo fdisk -l

Disk /dev/sda: 320.1 GB, 320072933376 bytes
255 heads, 63 sectors/track, 38913 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0xd935d935

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           1        2432    19530752   83  Linux
/dev/sda2            2432       38914   293037057    5  Extended
/dev/sda5            2432        2797     2928640   82  Linux swap / Solaris
/dev/sda6            2797        5228    19529728   83  Linux
/dev/sda7            5228       38914   270576640   83  Linux

the last one I want to convert to ext4 or some thing which  I can
use.In nautilus window it shows me lost+found a cross icon is marked.