what do the numbers after the : /dev/block/vold/179:xx mean?
These are the "major device number":"minor device number" (You can list them with cat /proc/partitions in adb). The major device number selects which device driver is being called to perform the input/output operation. This call is being done with the minor number as a parameter and it is entirely up to the driver how the minor number is being interpreted. The driver documentation usually describes how the driver uses minor numbers.

The sc-card is normally mounted by the volume daemon (vold). The output of mount shows you where the according mount points are.