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Show 194 OLDER PLIOCENE PERIOD, [Ch. XIV. ENGLISH MILES. 2 3 4 5 No. 48. ~V?lc~nic} A, Upper E!fel. ~ P1stnct B, Lower E1fel. ~ Points of ~ruption, with craters ~ and SCOrHI:l. ~Basalt. ~ Trachyte. j . I Brown coal. N.B. The country in that part of the map which is left blank is almost entirely composed of graywacke. There has been a long succession of eruptions in this cou~try, and some of them must have occurred when its physical geography was in a very different state, while others have happened when the whole district had nearly assumed its present configuration. The fundamental rock of the Eifel is an ancient secondary sandstone and shale, ·to which the obscure and vague appel1ation of c graywacke' has been given. The formation has precisely the characters of a great part of those grey and red sandstones and shales which are called ' old red sandstone' in Ch. XIV.) LAJlE·CRATERS OF TilE EIFEL. 195 England and Scotland, where they constitute the inferior member of the carboniferous series. In the Eifel they occupy the same geological position, and in some parts alternate with a limestone, containing trilobites and other fossils of our mountain and transition limestones. The strata are inclined at all angles from the horizontal to the vertical, and must have undergone reiterated convulsions before the country was moulded into its present form. Lake-Craters.-The volcanos have broken out sometimes at the bottom of deep valleys, sometimes on the summit of hills, and frequently on intervening platforms. The traveller often falls upon them unexpectedly in a district otherwise extremely barren of geological interest. Thus, for example, he might arrive at the village of Gemunden, immediately south of Daun, without suspecting that he was in the immediate vicinity of some of the most remarkable vents of eruption. Leaving a stream which flows at the bottom of a deep val1ey in a sandstone country, he climbs the steep acclivity of a hill where he observes the edges of strata of sandstone and shale dipping inwards towards the mountain. When he has ascended to a considerable height he sees fragments of scorire sparingly scattered over the surface, till at length on reaching the summit he finds himself suddenly on the edge of a tarn, or deep circular lake-basin. No.49. Tile Gemunden lllam·. This, which is called the Gemunden Maar, is the first of three lakes which are in immediate contact, the same ridO'e forminO' the b . b 0 amer of two neighbouring cavities (see diag. No, 50). On 0 2 |