16 PILGRIM GEOLOGY OF THE PERSIAN GULF. as the Hippuritic and Hormuz series, the two latter occurring as inliers within deep bays of the Nummulitic cliffs, which here are sandstones with thin-bedded limestones. Since we know that the lowest beds of the Nummulitics are probably no older than the Khirthar series, the age of these Hormuz rocks may be anything between the Upper Cretaceous and the Middle Eocene. The eastern limit of these beds seems to be the latitude of the island of Hormuz, and I have observed them on the Persian coast as far west as the island of Shaik Shuaib. They occur on almost all the Gulf islands as far west as the peninsula of Qatar, but whether they exist either on the mainland of Qatar, or on the coast of Arabia to the south and east of Qatar, is not known. I myself did not find them on the Pirate coast. They appear to have existed as a continuous tract of land in Eocene times, separating the Nummulitic areas of Bahrain and Persia. This land may have been depressed to some extent during Miocene times, but subsequent elevation and exposure to aërial denudation produced the irregularly hilly country, which the widespread subsi dence of comparatively recent times has left in the form of islands. The volcanic rocks of the series consist of rhyolites, trachytes, ash beds, and tuffs. In the island of Hormuz sedimentary rocks are very poorly represented as far as can be seen; here and there gritty sand stones, shales and carbonaceous limestones are visible amid the vast beds of rock salt and gypsum. In Hormuz the rock salt makes up as much as half the entire formation. It presents very much the appearance of being eruptive. It is associated with hæmatite, iron pyrites, sulphur, dolomite, and anhydrite. Owing to the subsequent solution of the salt the surface of the ground has fallen in, giving the hills occupied by the Hormuz series a singularly craggy aspect. Their almost entire barrenness increases the peculiarity of their appearance. In some localities salt is practically absent, as for example in the island of Bu Musa, where its place is taken by gypsum. Both gypsum and salt beds are of variegated colours, in which red predominates, due to the presence of red iron oxide (red ochre), which
