3'98 Kirwammi Society of Dublin, 



to Ecles's doctrines with observing, that the great princi- 

 ple upon which the whole is founded is demonstrably false. 



At the same nietf ing a paper, by Dr. Ogilby, (one of the 

 vice-presidents,) " On a Formation of Porphyry which nc- 

 cnrs in the counties of Antrim and Down," was read. The 

 paper was accompanied by a collection of specimens, illus- 

 trative of the scries from the older to the newer beds of this 

 formation. After some general remarks upon the porphy- 

 ries of the Werncrian Geognosv, which have been confined 

 to the class of primitive rocks, it was stated as probable, 

 in consequence of Professor Jameson havine recently dis- 

 covered transition and fltelz porphyries in Scotland, that 

 still more extended observation might develop a series from 

 the oldest or primitive porphyries of Werner, throuch the 

 transition and floetz observed by Jameson, to others of still 

 later formation, or approaching nearer to the oldest alluvial 

 products. A considerable extent of country between the 

 smnll towns of Doagh and Kells, in the county of Antrim, 

 called Sandy Braes, and which had been first noticed (though 

 never described) by the late celebrated Dr. Mitchell, consists 

 of porphyritic rocks. Dr. Ogilby has since observed a con- 

 siderable detached portion, which he considers of the same 

 formation, near the town of Newton Glens, on the NJ' 

 coast, and has also found traces of it near the towns of 

 Broughshane and Templepatrick, and at Killymorris in the 

 same county; and, from the specimens deposited in the 

 Dublin Society's Mtiseum, it would also appear to occur 

 near Hillsbro', in the county Down. 



After some remarks upon the aeneral appearances of the 

 hills composed of these rocks, which are low, irreaular and 

 obtusely conical in their form, the series of minerals was 

 described in the following order, commencing with the 

 lowest or oldest member he could disc )ver of the series. 

 1. Porphyritic clay-stone, the basis of which passes on the 

 one side into clay of little induration ; and on the other 

 into compact felspar, and rarely, a mineral approaching 

 in its characters to red jasper. 2. Felspar porphyry. 

 3. Porphyry with a basis of compact felspar and finely 

 disseminated hornblende, which may be called Greenstone 

 Porphyry. Some specimens of this rock showed a strong 

 tendency to the porphyry slate of Werner. 4. Pilchslono 

 and pearlstone porphyry, in some of the specimens of which 

 the passage of pearlstone into pitchstone was very distinct. 



A transition of the pitchstone into hornstone pt)rphvry 

 was also observable. The semi and common opal of dif- 

 ferent sliades of jellow, and apparently of cotemporaneous 



formation 



