Heron based his map on the topographical map that was being drawn by Morshead and his team, although for much of the time the region he was in had not yet been mapped so he had to transcribe his observations later. The scale was four miles to an inch (1:250,000). Heron discovered that the Tibetan plateau was intensely folded sedimentary Jurassic shale and Cretaceous limestone with an east-west strike with, he considered, the folding indicating movement from the north. The uppermost limestone, Cretaceous and later, contained fossils but the shale had little by way of fossils. Nearer to the mountains the shale was underlain by limestone (possibly Triassic or Jurassic) metamorphosed into crystalline form and into calcareous gneiss. In the vicinity of the high mountains the rock was biotite gneiss. The high peaks north west of Everest had granite intrusions and possibly the same would apply on Everest itself. He considered that the biotite gneiss was probably an igneous intrusion into the calcareous gneiss. There were no ores or minerals of commercial interest.