Last game session and umber hulk retreated from the group by burrowing into the earth. The party druid, not willing to let it go, summoned an earth elemental to follow it. Then, looking at the earth elemental description, we realised that it has no actual method of seeing when in the earth
. Other monsters of this type (Umberhulks, Xorn etc.) all have tremorsense or something similar. Am I just missing something in the earth elemental description?
I think this is obviously an oversight, as the alternative makes no sense - what do you guys think?

I think this is obviously an oversight, as the alternative makes no sense - what do you guys think?