1864.] TATE— CEETACEOtrS ROCKS OF IRELAND. 19^ 



Allan * (1821) noticed the prevalence of the White Limestone in 

 the north-eastern angle of Ireland, and its uniformly resting on the 

 Greensand or Mulatto stone. He also pointed out the extent and 

 position, as well as the general characters of the limestone, and those 

 of its altered portions. 



Bouef still later referred the Mulatto sandstone to the Graie tujfecm 

 of France, and the superior beds to the Oraie blanche. 



Griffith^ (1838) has referred to the relations of Ihe Secondary 

 rocks of the co. Antrim, and described their position, characters, 

 and area. 



Bryce§ (1837) added some further details, especially as regards 

 the relation of the Chalk to the Mulatto and underlying formations, 

 and the variation and thinning-out of the Mulatto in its progress 

 northwards. 



Of the labours of General Portlock || (1843) I have only to 

 notice, for my present purpose, that he made the first attempt to 

 particularize the palseontological characters of the Cretaceous beds. 

 The fossils, to the number of seventy-eight, he distributed into three 

 subdivisions of the " Chalk," as follows : — 



" 1st, Arenaceous, or glauconous, or ' Greensand.' 

 2nd, The Lower Chalk. 

 3rd, The Upper Chalk." 



The first division comprises the loose grey sandy beds referred to 

 at p. 110, and are evidently the Glauconitic sands and yellow sand- 

 stones of my section, here introduced for the first time. 



The second division he elsewhere designates as the Chloritous 

 Chalk (p. 109) and indurated Greensand, or the so-called Mulatto 

 stone (p. 110); and as such it accords with my lithological zone 

 No. 2 at p. 18. 



The lithological divisions of the Cretaceous beds, as given by Mr. 

 Bryce (1852) in the following quotation, are the same that I have 

 employed, though his paper was not known to " me until after the 

 preparation of this communication : — 



" The Cretaceous system is represented by the Upper Greensand 

 and Chalk, the Lower Greensand and Gault being absent. This 

 Upper Greensand consists of three beds : the lowest is a slightly 

 cohering sandy bed of a green colour, a true greensand ; the second 

 is a buff-coloured calcareous sandstone ; the uppermost is a grejdsh- 

 white impiu^e limestone, pervaded by chloritic grains. The upper 

 portions of this bed are often conglomerate, pebbles of quartz being- 

 imbedded. To these upper chloritous beds the workmen have given 

 the name of ' Mulatto,' which is often used to designate the whole 

 series in Ireland." He gives no further details, but adds (and here 

 I essentially differ from him), " Hard white chalk, apparently the 

 representative of the lower part of the Chalk series in England." 



* " Formation of the Chalk," &c., Trans. Eoyal Soc. Edinb. vol. ix. p. 393. 

 t Essai G^ologique sur I'Ecosse, p. 379. 



I Outline of the Geology of Ireland, p. 19. 



§ Trans. Geol. Soc. 2nd ser. vol v. pp. 78-80. 



II Loc. cit. p. 749. 



c2 



