Abstract
This paper gives a definitive description of the lithology and thicknesses of the Upper Middle Hecla Hoek rocks of Ny Friesland, Spitsbergen, arising out of Cambridge expeditions since 1951. The succession is the late Pre-Cambrian part of the Hecla Hoek Geosyncline, lying below the Tillite horizons and characterized essentially by limestones and dolomites.