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Proceedings of the Royal Irish Academy. 



•gneiss — and tte micaceous quartzite which dips away northward, to 

 form a synclinal basin with the Erris Head quartzites, as shown in 

 the section above given (p. 138). 



Limestone does not appear in the neighbourhood of the junction 

 here, just as it does not appear near the junction at Erris Head ; but 

 in following the boundary of the two groups eastward by Portnacally, 

 it is marked by the presence of limestone beds which reappear on 

 the same line on the eastern shore of Broad Haven, as well as at 

 Kilcommon and Glencalry, as before mentioned. Were the ground 

 not almost entirely obscured by peat, drift, and local surface coverings, 

 there is little doubt it would be found that the occurrence of lime- 

 stone characterizes the boundary zone between the mica-schist and 

 quartzite throughout, except in the western part of the Erris Head 

 peninsula, known as the Mullet. 



!N'ow, the mica-schist at present overlies the quartzite series east of 

 Eroad Haven, while at the west coast of the Mullet it occupies its 

 normal stratigraphical position, that is beneath the quartzite ; so that 

 we are obviously dealing only with two main series instead of three, 

 as might at first sight appear. A good section exhibiting the inverted 

 conditions of the groups is to be seen in Glencalry. Here the mica- 

 ceous quartzite may be followed bed after bed, dipping at 20° to 25° 

 towards a cascade, where the stream tumbles over a rugged bed 

 formed of mica-schist and limestone. The section here given repre- 

 sents the relations thus described and, diagramatically, that of the 

 quartzite group to the mica-schist and gneiss at Erris Head 21 miles 

 to the west. 



Fig. 3.— General Section from Erris Head hill (213) across Broad Haven eastward 

 to Glencalry hill (562) showing gneiss (G), quartzite {q), limestone 

 {1st), and mica-schist (m), faulted beyond overfold. 



I need only refer to the overfoldings to be seen in the corre- 

 sponding quartzite group in Donegal, and described in the Memoir 

 of Sheets, 1, 3, 9, &c., to indicate how fully we should expect to 

 find such inversions of the metamorphic strata as that above shown ; 

 and further, to expect minor puckerings of the strata, wliich would 

 account for repetitions of one limestone band, instead of several, 

 as might at first sight appear to be the case at Glencalry. A more 

 detailed section of the glen and river-bed is shown on next page. 



