 Many Irish mountains are also of geological distinction, most of them being formed in the Caledonian or Amorican era.These mountains, formed between 400 and 250 million years ago, would have been the same height as the Alps, but due to weathering, have become much smaller over time.In 2017 9,932,100 overseas tourists visited Ireland, a 3.5% increase over the previous years figure of 9,584,400.