1. Succession of Silurian Rocks in the South of Scotland.—The oldest fossiliferous strata yet detected in the Silurian district of the South of Scotland are the dark Graptolitic shales forming the well-known Moffat Series. The total thickness of this group is under 600 feet, but it is nevertheless capable of separation into three very distinct palæontological divisions, each characterized by a large proportion of peculiar fossils. The first of these divisions is of Llandeilo age, the second represents a portion of the Bala formation of North Wales, and the third, or Birkhill division, appertains, at least in part, to the epoch of the Lower Llandovery.