568 [Prtic. B.N.F.C. 



Ireland, ( a ) read before the Geological Society in 1863 and 1867 

 in which he declares the Waterloo section is the key to the 

 reading of the Liassic strata in Ireland, although the greatest 

 development occurs in Colin Glen, which is also referred to by 

 Gen. Portlock ( 4 ). It is interesting to recall that Prof. Tate 

 commenced his paper by pointing out that Gen. Portlock in 

 1843 first directed attention to certain beds linking the Triassic 

 and Liassic formations. He describes these beds as resting 

 directly on the Keuper marls, the upper or white Lias overlying 

 the Avicula Contorta section. In the white Lias section of the 

 Cave Hill, which is now much obliterated, he records the 

 occurrence of indurated marls exhibiting an oolite structure, 

 which disappears 6 feet from the dyke, this bed contained no 

 fossils. Surely the patch at Macedon Point may, without any 

 inherent improbability, be supposed to represent this white 

 Lias ; we have in it the oolite structure, most marked in the 

 immediate vicinity of the dyke and also much indurated. The 

 base of the patch at Macedon is not visible, but the Keuper 

 marls occur close by on the shore. Prof. Tate mentions that 

 in the Waterloo beds there is no line of demarcation between 

 the white Lias and the Avicula Contorta beds, several beds in 

 the series presenting grey marls with disseminated calcareous 

 particles, presenting an oolitic or even pisolitic structure. I 

 have unfortunately not had an opportunity of examining 

 whether any dykes occur in the Waterloo beds ; in the Cave 

 Hill section, and the supposed Rhaetic patch at Macedon, this 

 structure occurs close to the mass of the dyke. 



In conclusion I may mention that the patch occurs close to 

 the battery of stones which protects the sea-wall, commencing 

 from the north side of the most northerly extension towards 

 high water of the well known cross dykes, extends to a 

 short dyke also close to the sea-wall, and extends seaward along 

 the cross dykes. It may be also seen in indurated patches along 

 the margin of the dykes south of the point, many hundreds of 



3 Quart. Journ., Gcol. Soc, London. Vol. XXIII. (1867) p. 297. 



4 Repoit on the Geology of Londonderry (1843) PP- 49? 5^> 107. 



