Nofes on tJie Doleritic Intrusions of Euf^t Fife. 447 



These intrusions form marked topographic features to the south- 

 west of St. Andrew's, especially the last mentioned, which rises 

 into a tract of high ground over 600 feet above sea-level 

 and that ranges westwards for over a mile to near Ladeddie. In 

 the eastern part of this extent the mass is a non-ophitic olivine- 

 dolerite, which, traced towards the west, greatly increases its 

 content of iron-ores, interstitial glass also making its appearance. 

 Followed still farther west the glass continues to increase in quantity 

 until above Ladeddie the rock becomes a porphyritic olivine-basalt 

 (this rock must not be confounded in the field with the basalt of 

 the ash neck alongside). Some sections of this latter rock are 

 remarkably fresh, and show a pale structureless glass, or one 

 that is full of skeletal growths of iron ore, enclosing unaltered 

 idiomorphic crystals of labradorite, also strongly dispersing purplish 

 pyroxenes witla green centres that often show hour glass structure 

 and which are appreciably pleochroic. Larger crystals of olivine 

 and pyroxene lie in the rock, conferring upon it a porphyritic habit. 

 The only other rock masses known to the writer in East Fife 

 to contain such beautifully fresh glass as the above are those at the 

 roadside at Gillingshill, and at Longside, to the north-west of 

 Kennoway. But both these basalts, which mineralogically closely 

 resemble the western Drumcarrow rock, occur as intrusions in 

 volcanic necks, and this brings us immediately to the consideration 

 of a matter of special interest, viz. the probable monomagmatio 

 origin of the olivine-dolerites and vent basalts of the district. For if 

 the apparent mineralogic relationship between these masses be a real 

 relationshiji, and it appears real, then there is the probability that it 

 has an important bearing on the question of the geological age of 

 the volcanic vents of East Fife. The nature of this bearing may be 

 indicated as follows : There is considerable ground for believing 

 that the olivine-dolerites of East Fife represent merely the root 

 system of the volcanic manifestations that were known to have 

 occurred in this area in Upper Limestone times. If, as seems not 

 unlikely, that opinion be correct, then the great sheeting and 

 expansion of liquid igneous material that has taken place on or about 

 the horizon of the Lower Limestones would find ready explanation 

 as being connected with the depth of cover existing at that time. 

 For any igneous protrusion ascending from depths must ultimately 

 reach a height when by fluid pressure it will lift, or tend to lift, its 

 roof. Should the strata be horizontal, then the conditions become 

 eminently favourable for the production of great sheets. In the 

 above instance it appears possible that the zone of partition and 

 consequent insertion of igneous matter may have lain somewhere 

 about the stratigraphic level of the Lower Limestones. But the 

 introduction of any large volume of fluid igneous substance in the 

 manner indicated, has serious implication, namely, that the rocks in 

 the deeper part of the sequence would experieiice displacement and 

 rupture, sedimentation meanwhile being in progress uninterruptedly 



