KiNAHAN — A Neio Reading of the Donegal Rocks. 19 



east of Lough Swilly, at the extreme north of Inishowen, the 

 Older Period Rocks largely consist of micaceous quartzites and 

 highly quartzitic gneiss. 



In the north-east portion of the barony of Kilmaerenan there 

 is the Muckish quartzite/ over which is a sericitic series as- 

 sociated with limestones. This quartzite, and the overlying strata, 

 seem to me to belong to the Later Period Rocks, but I am not in a 

 position to speak positively, not having specially examined the 

 district; but during a rapid traverse I found that there is an 

 unmistakable inversion in the Muckish range, the older rocks now 

 lying over the younger ; but to the northward, in the ridge south 

 of Dunfanaghy, they are lying in their proper order, the younger 

 over the older. 



The Later Period Rocks may be grouped as follows {see Plate II. 

 for the order as seen in the Inishoiven promontory) : — 



[D] Lough Salt and Fanad quartzites, \ 



[D') *Lough Keel and Knockalla quartzites, ] ^""^^^ quartzite. 



[E] Cranford sericitic series. 



[F] Lough Keel schist series, ) n i. i • i. 

 [F') *Millford schist series, ) 



{G) Killygarvan volcanic series. 



[M) Killygarvan and Knoclybrin grit series. 



(/) Kintale and Lubber volcanic and limestone series. 



[J] Barn Hill grit series. 



[IT) Manorcunningham series. 



In the country to the west of Lough Swilly these different 

 groups of rocks have undergone considerable displacements, prin- 

 cipally by upthrusting from the south-east, the thrusting being 

 very conspicuous in the tracts of the Great quartzite. As succes- 

 sive small thrusts have pushed over the north-east portions of many 

 of these tracts on to the rocks to the northward, thus repeating 

 the beds over and over again, so that the quartzite now appears to 

 be much thicker than it is in reality. 



A marked displacement, but of a different type, is a great 

 downthrow to the north-west (bearing south-west and north-east), 



1 On MucMsh there is possibly an unrecorded outlier of Carboniferous rocks, as their 

 debris is found in the vicinity. 



C2 



