On the Palæontology of the Junction Beds of the Lower and Middle Lias in Gloucestershire

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Abstract
P revious to the writings of Messrs. Oppel and Wright on the classification of the various members of the Lias, that portion of the system which intervenes between the great limestone series of the Lower Lias below and the Marlstone above was referred to the Lower Lias; but these authors have drawn the line of demarcation between the Lower and Middle Lias through the mass of clays and shales which constitute the median portion of that system, the zone of Ammonites raricostatus being the uppermost member of the Lower Lias, and that of Ammonites Jamesoni the lowermost member of the Middle Lias. Now it has not been shown in any English publication that this separation harmonizes with the distribution of organic remains, and by the superficial reader the boundary-line may well be considered an arbitrary one; it will be my endeavour to establish the division of the Lower and Middle Lias as drawn by Oppel. That the zone of Ammonites capricornius is intimately connected with the Marlstone there cannot be a doubt, and in the Yorkshire Lias it has for many years been grouped with it; but as the zones of Ammonites Jamesoni and A. ibex , in this country, have usually been regarded as imperfectly fossilfferous, the necessary data for comparison being absent, the position of these zones in the Middle Lias has, with some degree of reasonableness, been questioned, more especially because the lithologieal conditions of the upper zones of the Lower Lias ( sensu stricto ) are repeated in the zone

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