THE OHDOVICIAN SYSTKM M7 



sandstones, mudstones, and shales. It is interesting to note that 

 the tup uf tin- highest (Dnunimick) group there is a thin bed 

 of grit which has yielded Staurocephalus globiceps, Trinucleus Euck- 

 I't/K/.i, a species of Palceaster and other fossils, associated with shales 

 containing Dicellograptus anceps and Diplograptus truncahu. The 

 graptolites show that these beds are equivalent to the highest 

 part of the Hartfell shale, but there are no limestones comparable 

 with those of Bala and Coniston. 



Beds of the Moffat type, dark shales and nmdstones, have been 

 traced all across Southern Scotland, from the Lammermuir Hills 

 through the northern parts of Selkirk and Dumfries and the 

 central parts of Kirkcudbright and Wigtown. Beds of an inter- 

 mediate type form a broad belt to the north of this, varying from 

 5 to 15 miles in width, from the Moorfoot Hills to the northern 

 part of Wigtownshire. 



No deposits of Ordovician age have yet been proved to exist in 

 the Central or Northern parts of Scotland. The only rocks which 

 may possibly be of that age are the green igneous rocks, green 

 shales, and jasper beds which occur between lines of fault along the 

 .-uii them border of the Central Highlands; but these are now 

 believed to be Upper Cambrian (see p. 97). 



5. Ireland 



Ordovician rocks occur in several parts of Ireland, as will be 

 seen by a reference to the map in Chapter IX. ; and they must 

 originally have been deposited over nearly the whole of the Irish 

 region. The largest area is that which spreads through Waterford, 

 Wexford, Wicklow, and Kildare, and is penetrated by the large 

 granitic massif which occupies so much of Carlow and Wicklow. 

 The sediments of this area have much resemblance to those of 

 Wal.-s. and may be regarded as a continuation of the latter, but 

 they are much more altered by subsequent igneous intrusions and 

 by concomitant earth pressures, so that they are greatly plicated, 

 crushed, and cleaved. 



The tract in the north, extending from Down to County 

 Cavan, presents a facies similar to that of the condensed series of 

 Southern Scotland, and the same type of graptolitic shale recurs 

 in the south-west round Lough Derg on the borders of Clare and 

 Tipperary. In the north-west, however (Galway and Mayo), there 

 is a very different set of beds of a more littoral character. 



Eastern Facies. The eastern parts of this area were revised 

 by Messrs. Egan and M'Henry of the Geological Survey during 

 the years 1898 and 1899. 17 They found that there was apparently 



