192 Dr. Berger on the Geological Features 



has stripped away the basahic masses which once covered them. 

 This opinion seems principally grounded on the resemblance between 

 these porphyries and those occurring in more ancient countries. 



Another opinion represents these rocks as subordinate members in 

 the floetz trap formation. In favor of this it is urged that the general 

 dip of the strata constituting the great basin of the basaltic area must 

 (unless we suppose them to have been affected by a great dislocation 

 and elevation) have carried the substrata on which the trap reposes 

 to a much lower level than that which is actually occupied by the 

 hillocks in question ; and it has been asserted as a corroborating fact 

 that the porphyry is actually seen to rest upon the basalt in one of 

 the ravines which traverses the district, while still lower at Temple- 

 patrick, the stratum of chalk on which the basalt really reposes makes 

 its appearance. 



The occurrence of similar rocks subordinate to floetz trap is by 

 no means unexampled in other countries. Near Newry a narrow 

 dyke of pitchstone porphyry extends for half a mile to the west, 

 and in a continuation of the same line clay porphyry occurs. This 

 dyke traverses sienitic rocks : an account of it is given in Dr. Fitton's 

 notes on the mineralogy of the vicinity of Dublin, p. 53. 



A singular formation of clay porphyry approaching to clinkstone 

 porphyry occurs near Newtonglens in Antrim, seemingly associated 

 with the old red sandstone ; it is particularly described in the note* 

 on the sections of the coast, appended to the present paper. 



