The rocks which form the Maltese islands have been at various times referred to very different parts of the Cainozoic group. At first they were all assigned to the Eocene, but a further knowledge of their fossils led to the transference of the whole series to the Miocene, in which system they have been included by most English writers. Herr Th. Fuchs, However, who first attempted any precise determination of the horizons of the subdivisions, correlated the Upper Limestone with the Leithakalk and the Blue Clay with the Schlier, and included the two lowest beds in the Oligocene. Dr Murray, however, in the course of his recent Memoir, has explained the striking palæontological differences between the faunas of the different deposits as due to altered conditions of formation rather than to lapse of time, and seems to follow earlier authors in including the whole series in the Miocene.

The Echinoidea of these deposits were originally described by Dr Wright in 1855,§ with additions and corrections in 1864; but since that time much work has been done on the allied faunas.

The fjord-like inlets or sea-lochs which form so conspicuous a feature in the scenery of the west of Scotland stand in marked contrast to the shallow, low-shored firths of the east coast. When Dr John Murray decided to extend the physical and biological work of the Scottish Marine Station to the west coast he foresaw that many interesting conclusions were likely to be derived from the study of these isolated sea-basins. Various papers, published by him and other workers, contain preliminary discussions of many of the phenomena observed, fully justifying the anticipations which had been formed.

For one year my work, as described in this paper, was carried out under the provisions of an Elective Fellowship in Experimental Physics of the University of Edinburgh, to which I had been elected in 1886; and subsequently by a personal grant from the Government Grant Committee for Scientific Research. The Committee also devoted several sums of money in payment of expenses in compiling this discussion. The Scottish Marine Station throughout gave the use of the steam-yacht “Medusa,” and the necessary apparatus.