  We investigate the Hi envelope of the young, massive GMCs in the star-forming
regions N48 and N49, which are located within the high column density Hi ridge
between two kpc-scale supergiant shells, LMC 4 and LMC 5. New long-baseline Hi
21 cm line observations with the Australia Telescope Compact Array (ATCA) were
combined with archival shorter baseline data and single dish data from the
Parkes telescope, for a final synthesized beam size of 24.75" by 20.48", which
corresponds to a spatial resolution of ~ 6 pc in the LMC. It is newly revealed
that the Hi gas is highly filamentary, and that the molecular clumps are
distributed along filamentary Hi features. In total 39 filamentary features are
identified and their typical width is ~ 21 (8-49) [pc]. We propose a scenario
in which the GMCs were formed via gravitational instabilities in atomic gas
which was initially accumulated by the two shells and then further compressed
by their collision. This suggests that GMC formation involves the filamentary
nature of the atomic medium.
