107 



seen to form sills or intrusive sheets, and are consequently 

 considered to more generally take this form. 



The peridotite, pyroxenite, gabbro, and diabase, form 

 a continuous series, passing by gradual transitions from 

 one variety to another, in the order named. In the case 

 of larger exposures, all of these rock types can sometimes 

 be found in a single intrusive mass. In other cases, the 

 differentiation is sharper, and peridotite passes into diabase 

 with only a few feet of transitional rock between. In 

 general, peridotite, or the serpentine derived from it, and 

 diabase, form the larger portion of a rock mass. At the 

 outer edges, the diabase, in places, passes into hornblende 

 porphyrite, and this occasionally into hornblende granite, 

 or aplite. 



The granite and aplite have usually, however, been 

 intruded a little later than the more basic rocks. The 

 edges of these acid intrusions are generally as well crystal- 

 lized as the central parts, showing that they were brought 

 in while the basic rocks were still heated. Occasionally, 

 too, an injection of diabase has taken place somewhat later 

 than the intrusion of the greater part of the mass. This 

 may be seen at Louise mountain, in Garthby, and probably 

 near Shipton Pinnacle, but such occurrences are not 

 common. 



The rocks of this igneous complex are generally 

 distributed in one or other of two different modes of arrange- 

 ment, according to the form, of the igneous intrusion. 

 They are arranged in order of decreasing basicity and 

 density : — 



(i) In sheets, from the base upwards. 



(2) In batholithic intrusions, from the centre out- 

 wards. 



Serpentine, or diabase may sometimes be much in 

 excess of the other rocks, and thus give an asymmetric 

 arrangement. But the more acid rocks, wherever present, 

 are, as far as known, invariably near the tops of sheets or 

 the margins of batholithic intrusions, and the basic rocks 

 in correspondingly opposite directions. 



In the case of sheets, the arrangement of the rocks 

 accords with the relative densities of the principal minerals 

 of which they are composed, and also with the order of 

 their crystallization. 



In the case of batholithic intrusions, the differentia- 

 tion from basic to acid extremes, from the centre outwards, 



