One factor suggests that if our cave was on the Llangattock scarp it might have had this barometric effect, and that is that this tends to effect very large cave systems. The caves that have entrances on the scarp are probably part of a system that is amongst the longest in Britain.

However, if it is true that the wind blew constantly out of our cave it seems unlikely that this was due to barometric changes. While the weather conditions at the time the Historia was written were probably worse¹ it is unlikely Britain suffered much more pressure variation.

This, then, suggests a Chimney Effect cave. An escarpment is the perfect place for this, as the caves can link the plateau above with the valley below. The only downside of this explanation is that there is no obvious air outflow or inflow on the plateau above the scarp at Llangattock, that is, all the obvious cave entrances are on the scarp. That said, any outflow need not be through a large and obvious hole.