A. McHenry — Trachytic Rocks of Antrim. 



261 



seemed to show that the trach3'te was later thau the Tertiary 

 basalt sheets of the lower division ; and, on further investigation 

 into this interesting subject, additional evidence was procured that 

 the trachytic eruption was older than the sheets of the upper 

 series, and was, so to speak, of mid-basaltic age. Subsequently 

 I accompanied the Director-General, Sir Archibald Geikie, on his 

 visit of inspection to this locality, and he approved of my views. 

 Professor Gilbert, of the United States Geological Survey, who was 

 with us at the time, also agreed with the conclusions arrived at. , 



The accompanying sketches and sections will serve to illustrate 

 the mode of occurrence of the trachyte and adjacent rocks. They 

 were made at the time of my first visit to the quarry. 



Fig. 1 shows the most important point in the evidence as to the 

 relative ages of the trachyte and basalt. It will be seen that the 

 trachyte during its eruption, in the form of a laccolite, swept 

 the eroded chalk surface of its usual superincumbent flint gravel 

 bed, which is composed of burnt chalk flints, chalk fragments, and 



Tis. 1. 





East end of Templepatrick Quany, county Antrim, showing position of Clbalk, 

 gravel bed. Lower Basalt, and Trachyte. From sketch made in May, 1888. 



red marly clay, and piled it up against the opposing and evidently 

 pre-existing barrier of basalt, on its eastern side. The columnar 

 structure in the trachyte is well marked, and has clearly converged, 

 during the cooling process, from the outside towards the centre of 

 the mass, while a beautiful and regular flow structure is apparent, 

 running parallel to its outward margin, as shown in sketch. 



Remnants of the flint-gravel bed are to be seen in a few pockets 

 and hollows of the eroded chalk surface, which were evidently left 

 behind in more or less sheltered places, while the igneous mass was 

 advancing. 



This gi'avel bed, where it is in contact with the trachyte, has 

 been baked and indurated into a compact and solid flinty mass, 

 while in every other instance in which 1 have seen it in its usual or 



