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It affords the thickest stratum of pure vegetable matter hitherto detected in any secondary rock in England. One seam of coal of good quality has been worked three and a half feet thick, and there are several feet more of pyritous coal resting upon it. Terebratula fimbria, Sowerby. Inferior Oolite marl. Rhynchonella spinosa, Schloth. Pholadomya fidicula, Sowerby. One-third natural size.
Let it be borne in mind that Avicula, Mytilus, Chiton, Natica, Patella, Trochus, Discina, Orbicula, Lingula, Rhynchonella, and Nautilus, all of which are existing genera, are given without a doubt as Silurian in the last edition of "Siluria;" while the highest forms of the highest Cephalopods are represented in the Lias by a genus, Belemnoteuthis, which presents the closest relation to the existing Loligo.
Although there are eight or more species of Ammonites and six of them peculiar to it, this genus is much less fully represented than in each of the other subdivisions of the Upper Cretaceous group. Terebratulina striata, Wahlenb. Rhynchonella octoplicata, Sowerby. Upper white chalk. Magas pumila, Sowerby. Terebratula carnea, Sowerby. Terebratula biplicata, Brocch. Crania Parisiensis, Duf.
Some of this same tribe of shells, such as Camarophoria, allied to Rhynchonella, Spiriferina, and two species of Lingula, are specifically the same as fossils of the carboniferous rocks. Restored outline of a fish of the genus Palaeoniscus, Agassiz. Beneath the limestone lies a formation termed the marl-stone, which consists of hard calcareous shales, marl-slate, and thin-bedded limestones.
Arctic shells, which formed so large a proportion in the Chillesford and Aldeby beds, are more rare in the Norwich Crag, though many northern species such as Rhynchonella psittacea, Scalaria Groenlandica, Astarte borealis, Panopaea Norvegia, and others still occur.
As usual in bone-beds, the teeth and bones are, for the most part, fragmentary and rolled. Orthis elegantula, Dalm. Var. Orbicularis, Sowerby. Rhynchonella navicula, Sowerby.
In illustration of shells having a great vertical range, it may be stated that in England some few species pass up from the Lower to the Upper Oolite, as, for example, Rhynchonella obsoleta, Lithodomus inclusus, Pholadomya ovalis, and Trigonia costata. Ammonites macrocephalus, Schloth. One-third natural size.
Let it be borne in mind that 'Avicula', 'Mytails', 'Chiton', 'Natica', 'Patella', 'Trochus', 'Discina', 'Orbicula', 'Lingula', 'Rhynchonella', and 'Nautilus', all of which are existing 'genera', are given without a doubt as Silurian in the last edition of 'Siluria'; while the highest forms of the highest Cephalopods are represented in the Lias by a genus, 'Belemnoteuthis', which presents the closest relation to the existing 'Loligo'.
Let it be borne in mind that 'Avicula', 'Mytalis', 'Chiton', 'Natica', 'Patella', 'Trochus', 'Discina', 'Orbicula', 'Lingula', 'Rhynchonella', and 'Nautilus', all of which are existing 'genera', are given without a doubt as Silurian in the last edition of 'Siluria'; while the highest forms of the highest Cephalopods are represented in the Lias by a genus, 'Belemnoteuthis', which presents the closest relation to the existing 'Loligo'.
Davidson on the British Brachiopoda, illustrates, in the first place, the tendency of certain generic forms in this division of the mollusca to be persistent throughout the whole range of geological time yet known to us; for the four genera, Rhynchonella, Crania, Discina, and Lingula, have been traced through the Silurian, Devonian, Carboniferous, Permian, Jurassic, Cretaceous, Tertiary, and Recent periods, and still retain in the existing seas the identical shape and character which they exhibited in the earliest formations.
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