Notices of Memoirs — Prof. W. King. 465 



and lias been referred to in the Survey maps and labelled in tbe 

 Survey collections as obsidian, doubtless from its black colour and 

 waxy lustre. In physical character it somewhat agrees with the 

 Chlorophaeite of Maculloch, but is entirely diiferent in composition, 

 which more resembles that of Delessite. From this, however, it 

 differs essentially in colour, hardness, streak, and specific gravity, 

 but it appears on the whole to belong to the ferruginous chlorite 

 group. Physical characters — Colour, velvet black ; hardness, 2 ; 

 brittle ; lustre, waxy to dull ; very slightly affected by acids ; occurs 

 at Carnmoney and Shane's Castle, near Lough Neagh. The chemical 

 composition of the mineral was given, and compared with those of 

 Delessite and Chlorophgeite. Its most remarkable characteristics are 

 its low specific gravity and its resistance to the blow-pipe — both 

 curious points, considering the large quantity of iron it contains. 

 The author proposed to call the mineral Hullite, after Professor 

 Hull, in commemoration of the valuable work he has done in eluci- 

 dating the microscopic mineralogy of the basalts of Ireland. Pro- 

 fessor Hull has examined the microscopic structure of the mineral, 

 and of the rock in which it occurs, and has described the appearance 

 presented by the mineral. Under the microscope it is of an amber 

 brown colour, nearly opaque. It permeates the whole rock, filling 

 the interstices, and inclosing the other minerals. It appears very 

 much to assume the character of chlorite, and is undoubtedly a distinct 

 mineral, and not a product of alteration. 



IX. — On the Age of the Crystalline Eocks of Donegal.^ By 

 Professor W. King, D. Sc. 



THE author said that the Crystalline Eocks of Donegal had been 

 carefully studied, both in their petrological and geographical 

 features, by Hampton, Scott, Harte, Griffith, Jukes, Blake, Harkness, 

 and others ; but among them some authors had succeeded in de- 

 termining their geological age by means of fossils. It was true that 

 the limestones in the Innis lower barony, in the northern part of 

 the count}'^, contained bodies which had been suspected to be the 

 remains of corals, but it was to be regretted that none of these 

 bodies, so far as is known, possessed sufficient evidence to enable 

 palceontologists to ofi'er a decided opinion as to their nature. Having 

 been lately in Donegal, besides examining their mineral and 

 structural character, he embraced the opportunity of endeavouring 

 to find if any of the rocks occurring in this county, especially the 

 Innis Lower Limestones, contained fossils. In the south coast 

 division of Donegal, between Lough Foyle and Lough Swilly, where 

 the least altered rocks prevailed, some of the limestones had ap- 

 parently undergone so little alteration that it might be expected 

 that they would retain the remains of any organisms originally 

 inclosed in them. The bodies taken for fossils and corals consisted 

 generally of white calcite, and they were occasionally found of a 

 cylindrical shape, with what appeared to be internal radiating plates 

 1 Read before Section C, Dublin, August 21, 1878. 



DECADE II. — VOL. V. — NO. X. 30 



