From the preceding observations it appears that the Avicula contorta beds, which lie at the base of the Lias, contain a fauna of a special character; several of the Conchifera are identical with species found only in the Upper St. Cassian beds and Kössener-Schichten of continental geologists. These remarkable strata are grouped by one class of observers with the Trias, by another with the Lias; the difference of opinion among continental geologists has arisen from the circumstance that the majority of the species have a Triassic fades, whilst a few only are said to pass into the Lias. In England, on the contrary, our grouping of the Avicula contorta beds has been based chiefly on their lithological character; and in part likewise from their being fossiliferous, and resting on the uppermost part of the unfossiliferous Red Marl; the fossils they were found to contain being assumed to be Liassic, from their proximity to the fossiliferous beds of the Lias. It has been stated by Sir Philip Egerton and Professor Agassiz, that the Fishes of the English Bone-bed are either special to that breccia, or belong to species which are well known in the Muschelkalk of Germany. General Portlock, who found these beds in the North of Ireland, stated that they contained Muschelkalk fossils; and Sir Charles Lyell, in his ‘Manual,’ from the determination of the Fish, placed the Bone-bed in the Trias. Lastly, I have now shown that the Conchifera are special to this zone, and that none of them