Evaporated/ evaporited milk!

Over the years, Ruddlesden geotechnical has done a lot of holes in Taunton and a lot of holes in Mercia Mudstone, but we have never come across as much gypsum* as this, producing milky-white flush returns with only a small proportion of the rock mass composed of the red siltstone typically associated with the Mercia Mudstone.

This would be interesting enough on its own, but the main geotechnical hazard on this site was not the gypsum (which was solid with no evidence of dissolution), but the overlying 5m of soft valley infill deposits (Colluvium).
Geology never ceases to surprise us. Luckily, if we knew what we were going to find, we would be out of a job!

* gypsum is an evaporite deposit laid down in shallow lakes in a hot desert during the Triassic Period, when southern Britain was at the same latitude as the Sahara - quite a bit different from present-day Taunton!