142 



Scientific Proceedings, Royal Dublin Society. 



is intrusive in the Dalradian (pre-Cambrian) sedimentary series ; like them, 

 it may be of pre-Cambrian age, and at the latest it may have been associated 



*-• 





Fig. 1. — Orbicular granite in normal biotite-granite of Mullaghderg, Tnisbiree Bay, Co. Donegal. 

 A large boulder of the orbicular rock lies in the foreground. Photographed by Mr. R. "Welch. 



with the Caledonian earth-folding of early Devonian times. At Mullaghderg 

 a small patch of the granite, merging on all sides into the normal type 



