First off, most of Ireland's geography and soil were greatly impacted by glaciers. These giant forms of ice changed the landscape drastically. Besides the high impact of the glaciers themselves, the water from the melting ice also impacted the landscape and soil.
The soil itself was pushed, plunged, and shredded all throughout the land. Soil was mixed, boulders were buried, and mountains were leveled. The change was so drastic that rocks from places farther away were even deposited into Ireland's earth.
When the glaciers receded, the sediments they had gained were also deposited onto the soil, creating a newer, younger soil (as far as soil goes). Water caused by the melting ice also created divots and new rivers. (Hogan, 2003)
Here is a video about the glaciers in Ireland.