The nearest known pre-Cretaceous rocks to Jamaica are Jurassic in Western Cuba, and Carboniferous in Colombia, Venezuela, and Honduras, all about 500 miles away. The evolution of Jamaica seems to have been somewhat as follows. Andine (?) orogenesis on or near the site took place, accompanied by magmatic invasion; the rocks are nowhere seen “in situ”, but they have supplied pebbles of granite, granodiorite, porphyry, hornfels, vein stuff, and limestones, more or less foliated or marmorized, but not gneisses nor schists. There is no evidence that any of them are older than Cretaceous, but they go to form the oldest beds of the island, the massive Blue Mountain purple conglomerates whose composition varies from place to place and of which no natural base is seen. Interbedded with these conglomerates are fossiliferous shales and Rudist limestones of Upper Senonian to Maestrichtian age. Low down, however, there is in Eastern Jamaica a bed of algal and foraminiferal limestone, without Rudistae, which was partly torn up and incorporated as rolled pebbles in the conglomerate. Some of these pebbles contain Camerina dickersoni Palmer, a foraminifer of Upper Cretaceous age, so the pebbles are but little older than the conglomerate containing them. Laramide orogenesis took place and this series was invaded by granodiorite and other intrusions. The uplifted area was eroded and some of the igneous and associated Cretaceous rocks exposed to denudation. Depression occurred and Lower or Lower Middle Eocene Carbonaceous shale or Richmond Beds, a Flysch-like series of limestones, shales, and conglomerates, were deposited.

The term pseudodeltidium was proposed by Bronn (1862, p. 242) for the shell-plate covering the delthyrium, or triangular opening between the teeth, in the ventral cardinal area of those brachiopods now assigned to the order Protremata. It is typically developed among the “family” Strophomenidae, of which it is a diagnostic feature, as a convex arch overhanging the interior of the ventral valve (Text-fig. 1A). In the embryo, the pseudodeltidium is secreted as a single unit when the shell is first formed, and is therefore not homologous with the deltidium (von Buch, 1834, p. 15) of the order Telotremata, since this is formed in the post-embryonic period as two separate plates which may subsequently coalesce (Beecher, 1892)

Edale lies in the valley of the River Noe about 3 miles north-west of Castleton. Near Edale End, about 2½ miles below the village, the Noe turns from a nearly east and west course to a nearly north and south course past Hope to join the River Derwent. In the neighbourhood of Edale the floor and lower flanks of the valley are formed of black shales known as the Edale Shales; they are overlain in succession by the Mam Tor Sandstones, the Shale Grit, the Grindslow Shales, and the coarse Kinder Scout Grits which form the great plateau of the Peak and the precipitous edge of Kinder Scout. North of the Edale valley the Mam Tor Sandstones reappear below the Shale Grit in Ashop Dale and Alport Dale. They occur also to the west of the valley in two narrow inliers just north of the railway in Roych Clough and Moor Clough.

Most of the Cambrian of Arvon has the “Caledonian” strike which is dominant in Snowdonia. But there is a tract at Tregarth, about a square mile in extent, where the beds trend in any direction: that is, have no strike at all. Nothing in the beds themselves is any explanation whatever: there seems no reason for this anomaly. We have to seek an explanation in the underlying floor, and there, I think, we win some light. That floor has more than one component: Mona Complex and Arvonian. In the chapter of the Anglesey Memoir on the Age of the Mona Complex, I have thrown out a suggestion (then in explanation of nothing but the pebbles), that hills of Gwna Quartzite stood up through the Arvonian lavas. Now, in the great conglomerate of the crest and dip-slope of Y Pare, pebbles of quartzite are so numerous as to outnumber those of the rhyolite. It seems legitimate to infer that, underneath this Tregarth tract, these buried knobs of quartzite were exceptionally numerous and exceptionally high, and made the sub-Cambrian floor so uneven that the beds which rested on it could not acquire the usual strike, but were driven hither and thither, in all sorts of irregular ways. The same irregularity, though to a somewhat less degree, affects the Arvonian tuffs themselves.

This description is based on observations made during several months' work during 1938 and 1939, undertaken for the Government of the Somaliland Protectorate in connection with water-supplies in the barren Zeila Plain.