The first part of this paper refers to the relations of the hypersthene rock of the Cuchullin Hills to the adjoining formations.

The author undertook the observations here detailed without the slightest view to publication. He made only brief notes on the spot, collected but few specimens, and drew the first sketch of a map which accompanies the paper, for his own amusement and information. Finding, however, that the published writings of geologists contained little or no notice of some facts which he had clearly established, he undertook this paper as a groundwork for future and more systematic researches.