As part of a survey of H i \lambda 21-cm emission in the Southern Milky Way , we have detected two large shells in the interstellar neutral hydrogen near l = 279 ^ { \circ } .
The center velocities are +36 and +56 km s ^ { -1 } , which puts the shells at kinematic distances of 7 and 10 kpc .
The larger shell is about 610 pc in diameter and very empty , with density contrast of at least 15 between the middle and the shell walls .
It has expansion velocity of about 20 km s ^ { -1 } and swept up mass of several million solar masses .
The energy indicated by the expansion may be as high as 2.4 \times 10 ^ { 53 } ergs .
We estimate its age to be 15 to 20 million years .
The smaller shell has diameter of about 400 pc , expansion velocity about 10 km s ^ { -1 } and swept up mass of about 10 ^ { 6 } solar masses .

Morphologically both regions appear to be shells , with high density regions mostly surrounding the voids , although the first appears to have channels of low density which connect with the halo above and below the H i layer .
They lie on the edge of the Carina arm , which suggests that they may be expanding horizontally into the interarm region as well as vertically out of the disk .
If this interpretation is correct , this is the first detection of an H i chimney which has blown out of both sides of the disk .