Vol. 57.] FROM THE ISLIND OF AREAX. 239 



itself is sometimes, as in the first specimen examined, so much 

 altered as to be saccharoidal in character, and with little or no trace 

 of organic structure. Other specimens, however, have, under the 

 microscope, all the appearance of Chalk, being very largely composed 

 of foraminifera, and chiefly of the common Glohigerina. Inter- 

 mediate conditions of alteration are to be seen in other specimens, 

 all of which may be matched by examples of Chalk from Antrim. 

 Indeed, the similarity is so close that, even without further evidence, 

 this Arran limestone would be referred to the Chalk ; but, fortu- 

 nately, certain organisms have been detected in both the limestone 

 and chert which remove any doubt that may have existed. 



Fossils from the Arran Chalk, 



Bwceranms (piece of shell showing prisms). 



Poljzoa (several specimens, perhaps Entalophora and Esckarino^).. 



Echinoderm (fragments of). 



PorosphcBra globular is. 



Hexactinellid sponge-fragments (? Plocosci/phia\ 



Tetractinellid and other spicules. 



Glohigeriim cretacea (and other species), 



Texiularia, etc, 



I desire to thank Dr. G. J. Hinde, F.R.S., for having kindly 

 examined the macro- and microscopic specimens of Arran limestone 

 and chert, and for allowing me to say that he endorses what has 

 been stated above as to their being of Chalk age. 



4. Conclasion. 



The isla«id of Arran is fai? from any locality where strata, of 

 Jurassic or Cretaceous age are now found in place, the nearest 

 locality being in the North-east of Ireland, which is about 40 miles 

 away, where there are strata corresponding in a, remarkable degree 

 with the masses met with in Arran. 



The Secondary rocks of the N'orth-east of Ireland, which had 

 already been made known by Portlock,^ were described more fully 

 by Prof. Tate in 1863,^ and in still greater detail in 1867.^ In 

 these papers it is shown that Hhaetic beds, including the Avlcula 

 contorta-^hdle^ and the White Lias, rest upon older Triassic rocks 

 and are overlain by Lower Lias, in which four distinct zones have 

 been distinguished, namely, those of Ammonites planorbis, Arnm^ 

 angulatus^ Amm. Buoklandi, and Belemnites acutus. The uppermost 

 of these zones is succeeded by Upper Cretaceous beds, Greensand, 

 and hard Chalk,* and this again by basalt. Prof, Tate ^ has recorded 

 undoubted Middle Liassic fossils from Eallintoy, but apparently 

 from Drift, as hitherto they have not been found in place. 



^ ' Report on Geol. of Londonderry, &c/ 1843. 



^ Quart. Journ. Greol. Soc. vol, xx (1864) p. 103. 



3 Ibid. vol. xxiii (1867) p. 297. -» Tbid. vol. xxi (1865) p. 15. 



^ Ibid. vol. xxvi (1870) p. 324. 



