The present communication deals with a peculiar series of rocks found in association with the Tertiary sediments so extensively developed in south-west Persia at the head of the Persian Gulf. At one or two localities in that region the marls and limestones are baked, fused, and in some cases so thoroughly recrystallized that at one time they were suspected to be igneous material arising from localized volcanic action. Careful examination of the field occurrences has, however, failed to disclose any trace of volcanicity, whilst petrographical and chemical examination has shown that even the most coarsely crystalline types bear no resemblance to any known igneous rock.

My attention was first directed to these rocks by Mr. H. T. Mayo in 1926 when I was permitted to examine the material collected by Mr. B. K. N. Wyllie, to whom belongs the credit of first discovering these apparently unique occurrences, and to visit the localities, where additional material was obtained. The cause of the alteration of the sedimentary rocks at these localities is no longer operative, and is not apparent; that it may most probably be ascribed to the combustion of gas or oil long since extinguished has been made clear by the subsequent investigation of other localities where similar rocks have been, and are being, exposed to such action and have undergone similar changes in structure and mineral composition.