KiNAHAN — A New Reading of the Donegal Rocks. 27 



as can be seen by comparing the accompanying plotted vertical 

 section of the two series. (Plates Y. and YI.) 



The Cranford sericitic series is from over one thousand to one 

 thousand five hundred feet thick, and is made up almost entirely 

 of sericites, which have in them subordinate limestones and dolo- 

 mites, with lenticular quartzites. In it the limestones and 

 dolomites at the different localities occur on different horizons, 

 and are from a few inches to many feet in thickness, usually not 

 more than twenty feet, but in a few places they are massive. At 

 Cranford there are massive limestones and dolomites, and these 

 continue for over a mile towards the south-west ; then for about 

 two miles there is scarcely any limestone until the Grolam quarries 

 are reached, where the limestones and dolomites are again massive, 

 but only for a short distance ; and this is the character everywhere 

 else ; in one place being conspicuous, and elsewhere nearly disap- 

 pearing. 



This sericitic series is present everywhere in the baronies of 

 Inishowen, Kilmacrenan, and Boylagh above the Great quartzite. 

 On the other hand, the Lough Salt Limestone hornhlendite series is 

 always a regular alternation of diorite (hornblendites), limestone, 

 and schist ; and where well developed, as it is to the south-east of 

 Lough Akibbon, it is about one thousand feet thick. It is not found 

 in Inishowen in connexion with the Grreat quartzite ; nor in con- 

 nexion with the long exposure that extends from Ballymastoker 

 Bay, Lough Swilly, south-west to Glen Swilly, a distance of over 

 twenty-two miles. At Lough Salt, however, the Grreat quartzite 

 has been brought into contact with this series by faults; the 

 quartzite towards the north-east being upthrust on to it, while 

 towards the south-west the quartzite has been let down against the 

 limestone hornhlendite series. A little south-west of Lough 

 Salt the Limestone hornhlendite series parts company with the 

 quartzite, and for over eight miles towards the south-west it can 

 be seen as a group underlying a thick schist series. South-east of 

 Loughakibbon {see vertical section, fig. 2, Plate YI.) the rocks 

 are well exposed in a continuous section, without any faults, so 

 that by no possibility could the quartzite ever have existed here, 

 and be now concealed by faults. South of Gartan Lake (sheet 16), 

 the Boulder-beds in the north-east portion of the Knockanteenbeg 

 outlier were deposited on the upturned rocks of the Limestone 



