301 



Again, at Aughnahough (Fig. 1 ) the succession of the layers is not like 

 that at White Head ( Fig. 5) ; nor like that at Garron Point, (Fig. 4) ; 

 nor like that at Fair Head, in Murlogh Bay (PI. XXVI.) ; nor like that 

 at Bengore Head, near the Causeway (PI. XXIV. ). The section in all 

 those localities are widely different ; and even the layers of trap in 

 the same section — say at Garron Point, or at Bengore Head — are not 

 alike. There are alternate hard and soft layers ; sometimes a layer of 

 bole or ochre ; sometimes hard, black trap ; sometimes soft. A layer 

 is often seen in form of a lenticular mass, and thins out to nothing ; 

 then is succeeded horizontally by another ; and this is the case, 

 especially where they are thick. The trap of Antrim, therefore, accord- 

 ing to the view I take of it, does not consist of one great flow, but of 

 many different flows, coming from different sources. Since, then, there 

 is no regular succession from the chalk upwards, the few kinds I 

 may select as descriptive rocks I will arrange and describe in alpha- 

 betical order. I shall divide the trap rocks into eight kinds, which 

 will include the most extensive, and the most easily recognized ; and 

 I shall point out a few localities where each kind is well developed, 

 and any other matter I know in each locality that may be of interest 

 to the geologist. 



The varieties are : — 



1 . Amorphous trap. 



2. Brecciated trap. 



3. Columnar trap. 



4. Concretionary trap. 



5. Greenstone. 



6. Ochre, or bole. 



7. Tabular trap. 



8. Wacke. 



1. Amorphous Trap. — This is the hard kind, which crowns many of 

 the highest hills. It appears to be the upper layer, being next the 

 surface of the land in most places ; but it is also common in the middle 

 layers of a section. Its layers are of indefinite thickness, being some- 

 times 5 feet; sometimes 50 feet thick; and it occurs in irregular, 

 lenticular masses mostly. It is frequently quarried on the road sides, 

 for the use of the roads ; and an excellent material it is. The features 

 of all those hard traps — the amorphous, the brecciated, the columnar, 

 the concretionary, and the tabular, are easily recognized on the great 

 scale, in the hills ; but when broken into small fragments, such as are 

 used on roads, they cannot be well distinguished from each other in 

 hand specimens. In PL XXIV., the beds Nos. 1, 2, 3, are characteristic 

 of this kind. 



2. Brecciated Trap. — This kind occurs in layers of from 10 to 50 

 feet in thickness on the north coast. It is not common in the interior 

 of the country. It is plentiful in the vicinity of the Giant's Causeway. 

 The high precipice to the east of the little road that leads from the 

 hotel down to the Causeway is composed of it. There are many large, 

 roundish masses of it on the shore, at the water's edge, about the 

 Causeway itself, which tumbled down from the adjacent cliff; and the 

 fragmentary appearance they present is very characteristic of this kind. 

 There is a layer mostly composed of this rock, between the two princi- 



R. i. a. proc. — vol. x. 2 s 



