18 PROCEEDIlirGS OP THE GEOLOGICAL SOCIETY. [NoV. 9, 



Greeiisand ; but, as observed by D'Archiae*, " no part represents the 

 Gres-vert inferieur, as supposed by Brjce;" while Professor Oldliamf 

 comes to the same conclusion, on the authority of McAdam, "who 

 has found no representative of the Lower Greensand in that district." 



PortlockJ (1843), mistaking the age of the fossils, states that 

 " the true Lower Greensand, containing Pecten quinquecostatus, P. 

 cequicostatus var. longicoUis, Inoceramus Hamiltoni, &c., is found on 

 the eastern chalk- escarpment in the county of Antrim." 



Professor Forbes § thought that the Upper Greensand of Ireland 

 was more nearly allied to the Gault by its fossils. As regards the 

 Glauconitic Sands, such was also my opinion || until recently, but 

 my reasons for abandoning this view are given at p. 22. 



III. PtEVIEW OE THE WeITINGS OF PREVIOUS AlTTHOES. 



The Cretaceous beds of Ireland may be divided into the following 

 lithological zones in descending order ; but, convenient as they are, 

 they do not accord, as wiU be shown in the sequel, with the palseon- 

 tological horizons. 



Lithological Divisions of the Cretaceous Beds. 



1. " White Limestone " with flints. 



2. Chloritic Sandstone and Sands — " Mulatto Stone." 



3. Yellow Sandstones and Marls. 



4. Glauconitic Sands. 



Whitehurst^ (1786) was the first to regard the White Limestone 

 as " similar in appearance to a stratum of chalJcJ' 



Hamilton** (1790) observes that " the White Limestone in colour 

 resembles chalk, but, in hardness, exceeds it : like chalk, it abounds 

 in iiTegular nodules of flint." He further very accurately deflned 

 the boundaries of this formation, and gave important observations 

 upon the imbedded flints. 



Sampsonft (1814) further, though confusedly, recognized a sand- 

 stone below the White Limestone. 



Conybeare JJ (1816) more clearly exhibited the order of succession 

 of the Cretaceous strata, and referred the Mulatto sandstone under- 

 lying the Chalk to the horizon of the Upper Greensand. " It agrees 

 altogether in its character and fossils with green sandstone, which oc- 

 curs in a similar geological position underlying the Chalk in England " 

 (p. 130). He, however, referred the White Limestone to the age of 

 the Lower Chalk, thus : — "It agrees exactly with the lower beds of 

 the EngHsh Chalk." 



* Histoire des Progres, vol. iv. p. 8. 



t Journ. Geol. Soc. Dublin, vol. x. p. 97. 



X Eepoi't Geol. of Londonderry, &c., pp. 109 and 139. 



§ Jukes's Maniial of Geology, 1st edit. p. 514. 



II Quart. Journ. Geol. Soc. vol. xx. pp. 103, 108, &c. ; Geologist, 1863, p. 444. 

 ^ Original State, &c., of the Earth, 2nd edit. pp. 248, 259, and pi. 6. fig. 2. 

 ** Letters, Northern Coast of Antrim, part i. pp. 3, 5, 6; part ii. pp. 93-98. 

 ft Expl. Chart and Survey, co. Derry, p. 84. 

 U Trans. Geol. Soc. vol. i'ii. pp. 129-131, 167-173. 



