GSNI 250K Geology

250k Bedrock Geology A 1:250,000 map showing the main geological bedrock divisions in Northern Ireland. The data comprises the bedrock geology, which represents the outcrops (at surface) and subcrops (at near-surface, beneath superficial deposits) in Northern Ireland. For each rock unit there is a brief generalised description showing the major rock group, rock type and age under the following headings. LEX_D: The name of the selected area. This can be a group, formation or igneous intrusion e.g. dyke. LEX_RCS: Map code as it appears on the published 1:250,000 map. RCS_D: The name of the dominant types of rock (lithologies) in the different areas shown on the map e.g. granite. The names of the rock types given here are often generalisations, appropriate for the large areas of geological coverage at this scale. These areas may include a number of different geological formations whose distribution can only be portrayed on more detailed geological maps. RANK: Identifies formations and groups. Min_Time_D and Max_Tim_D: The age of the rock unit in terms of periods, relatively smaller units of geological time e.g. Carboniferous, Jurassic etc. Some of the map areas include rocks with a range of ages and these are shown as such e.g. Triassic to Cretaceous. The oldest metamorphic rocks are described as Moinian and Dalradian. The rocks range in age from those deposited relatively recently, some 2 million years ago, back to ancient and highly altered Precambrian rocks over 2500 million years old. In broad terms the youngest rocks are found in the south and east of the UK, the oldest in the north and west. 250K Superficial Geology This layer shows the superficial (drift) geology of Northern Ireland at 1:250,000 scale. 250K Bedrock Lines This layer shows bedrock features such as faults at 1:250,000 scale.