658 ME. E. R. C0WPER REED ON THE [Nov. I9OO, 



The description of the igneous rocks is here given in the first place 

 according to the main petrological types. After having examined 

 the available information as to the relations of these tj r pes, we shall 

 be in a position to determine their age and the sequence of events. 

 The rocks of the same petrological type must not be assumed to 

 belong necessarily to the same age. For the investigation of their 

 minute characters over 500 sections of these rocks for the micro- 

 scope have been prepared. 



II. Geographical Distribution and Geological Development 

 of the Rocks. 



a. The Felsitic Rocks. 



It will be convenient to describe all the felsitic rocks together, 

 though they include many different petrological types and belong to 

 several periods of effusion. Their modes of occurrence, relations, 

 and characters are so various and complicated, that it will be 

 necessary to enter into considerable detail before we can proceed to 

 distinguish their different ages, and classify them into separate 

 groups. In addition to the extensive and multifarious development 

 of the felsites as flows, veins, sheets, and dykes, there are also 

 important masses of tuff and agglomerate with necks, etc. Accord- 

 ingly the geographical distribution of these rocks will be first 

 described, commencing at the easternmost exposure and thence 

 working westward. 



Newtown Head. — At Newtown Head, near Passage, there is 

 a considerable development of intrusive felsite at the base of the 

 Raheen Series. Tongues of a bluish-grey flinty felsite are first 

 seen penetrating the tuffs, etc. of this series, and as they are 

 followed southward they are found to swell out into thick beds, 

 overlying and piercing a mass of diabase. 



A small stack of tough, unbedded, felsitic ash stands up on the 

 foreshore, and in the cliffs behind is seen a good section of the vent 

 from which the felsite flowed (fig. 1, p. 659). The diabase near 

 its contact with the felsite is found to be considerably crushed ; a 

 narrow crush-zone of soft rotten rock marks the actual line of 

 contact, and can be traced right over the rocks of the foreshore from 

 one side of the vent to the other. In parts the rock is actually 

 brecciated, and there was formerly a section exposed showing large 

 masses of the breccia enclosed in the felsite. In another place a 

 tongue of the felsite was observed protruding into the diabase. The 

 breccia appears to' have been formed by the first explosion which 

 drilled the hole through the diabase and associated rocks, the felsitic 

 lava subsequently welling up, filling the pipe, and giving off lateral 

 tongues. The relations of this vent and the felsite make it obvious 

 that this was the latest outburst of volcanic activity at this spot. 



Tramore Bay. — Leaving now this locality, and proceeding to 

 the west side of Tramore Bay, we meet with a different develop- 

 ment of felsitic rocks. With the exception of a few comparatively 



