482 British Association for the Advancement of Science. 



veins are frequently observable, such as their passage through the 

 adjacent schists, detached portions of which are often enveloped 

 in their substance, and the change they effect in their structure. 

 Mr. Griffith next described the older and newer trap districts, men- 

 tioning many interesting particulars connected with them, such as the 

 capping of quartz rock by greenstone, the concentric arrangement 

 of the beds of greenstone in Donegal, and the occurrence of quartz 

 rock between two beds of greenstone, the quartz being columnar, 

 the trap, above and below it, not. In Slieve Gullin greenstone and 

 granite were stated to be actually mixed together, whilst in Carling- 

 ford the contact of the sienite (or greenstone) with the granite is 

 concealed by debris. After noticing briefly the ochre beds which 

 so often separate the beds of basalt, and expressing his belief that 

 the trachytic porphyry of Sandy Brae in Antrim was nothing more 

 than this ochre indurated by heat, Mr. Griffith adduced the fact of 

 beds of sienite traversing the cliffs of Murloch Bay, and containing 

 detached portions of chalk, as proof that the sienite was posterior 

 in appearance to the chalk ; and gave it as his opinion that all the 

 crystalline rocks had been fused, and in most cases projected from 

 beneath through the sedimentary rocks, the appearance of regular 

 strata being due to their projection in a direction parallel to the 

 strike of the beds. 



Mr. Griffith stated the existence of an extensive marl deposit in 

 Wexford, some of the shells of which appeared to correspond with 

 those of the crag. 



On a small isolated Patch of Granite which occurs in the Cotmty of 

 Cavan. By Lieutenant Stotherd. 



The superficial extent of this granite is about seven square miles, 

 and it is separated from the nearest group of primitive rocks, that of 

 the Mourne mountains, by the grauwacke or transition schists. This 

 small district is entirely surrounded by transition and secondary 

 rocks, and exhibits all those changes in the structure of the sedimen- 

 tary rocks which are usually observed on their approach to, or con- 

 tact with, rocks of a decidedly igneous origin, the schists becoming 

 indurated and often changed to quartz rock. The appearance of 

 primary rocks so far removed from any of the greater masses is 

 extremely important in geological speculation, and assists in this 

 instance in explaining the broken and detached character of the 

 schistose hills, and the induration of many of their strata, since it is 

 probable that the granite is at no great distance from the surface 

 in the whole space between the Cavan primary rocks and the 

 Mourne mountains, of which they may be considered an extension. 



Copies of a map of the geology of the environs of Dublin, accom- 



?anied by a memoir, were presented to the Section by Dr. Scouler, 

 'rofessor of Geology to the Royal Dublin Society. 



