P ortlock in his ‘Survey of Londonderry’ makes no mention of the presence of the Middle Lias in Ireland; and an examination of the species of fossils collected by him proves that no higher member of the Jurassic series than the Lower Lias is represented by them. In a former communication I demonstrated the presence of the whole series of the Lower Lias, and, till recently, was unaware of the occurrence of strata newer than that formation. Mr. William Gray has sent me several blocks of a grey, marly, micaceous sandstone, charged with organic remains of Middle Liassic age; these were obtained near the town of Ballintoy, “in fields and cultivated patches of drift,” and conjectured by the discoverer to have been derived from the immediate vicinity; but up to the present time they have not been referred to their parent site. With the exception of Plicatula spinosa , Avicula novemcostæ , and Rhynchonella variabilis , which range throughout the Lower and Middle Lias, the majority of the determined species indicate an horizon below the Marlstone but above the highest beds of the Lower Lias. The close similarity in lithological composition, and in part in fossiliferous contents, between the Pabba shales and the blocks found at Ballintoy suggests the probability of the latter having been transferred during glacial times from the Hebrides. Nevertheless the sandstone blocks from Ballintoy belong unquestionably to the Middle Lias, and appertain to the lower division, which includes the Jamesoni -bed, the Ibex -bed, and the Capricornus -bed, and are contemporaneous (if not.