1866.] DUiN-CAN — INEEA-LIAS CORALS OP SOUTH WALES. 17 



more distinct than the lithological and palaeontological characteristics 

 of the Ammonites- BucMandi beds and of those now under considera- 

 tion. The lithological characters of the Brocastle beds have just been 

 described; and Mr. Tawney may be thus quoted with respect to those of 

 the other series. He remarks on the lithology of the Southerndown 

 series, " This series differs lithologically from the Sutton Stone in 

 the beds being much harder and more irregularly bedded, and they 

 are frequently subcrystalline and separated by thin arenaceous 

 partings; again, the fragments of black chert are more sparingly 

 scattered. The Sutton-Stone beds differ much in texture : some arc 

 fine-grained white limestones; others are softer and very shelly; some 

 are yellowish-white, and at the upper part are pale grey and be- 

 come gradually harder. The conglomerate at the base consists of 

 rolled pebbles of Carboniferous Limestone, very numerously imbedded, 

 with occasional pieces of chert in a soft fossiliferous white matrix. 

 The beds above the conglomerate contain shattered fragments of 

 black chert " *. The differences in the lithological composition of the 

 Brocastle, Southerndown, and Sutton beds are appreciable ; but they 

 have those common characteristics which separate them from the 

 Lower Lias strata with Gryplima incurva. The Lima-beds, as these 

 last are called, are earthy limestones, separated generally by argilla- 

 ceous shales; they are not conglomeratic, and do not contain any 

 fragments of black Carboniferous chert. 



The palaeontological differences between the beds under considera- 

 tion and those containing Ammonites BucMandi (the Lima-beds) 

 are very great. Not one species of the coral-fauna of Brocastle 

 has as yet been found in any beds of the Ammonites-Bucldandi zone 

 in any part of Great Britain or elsewhere. The same holds good 

 with regard to the Sutton Stone and the Southerndown beds. The 

 small list of Mollusca which I have given from the Brocastle beds has 

 not the facies of the fauna of the Ammonites-Bucldandi zone ; the 

 same is the case with regard to the Mollusca of the other beds. All 

 these beds form part of the Liassic formation, and have therefore 

 some species in common. The great bulk, however, of the Brocastle, 

 Sutton, and Southerndown Mollusca are peculiar to a definite 

 horiaon, and but a few species pass upwards into those beds of whose 

 lithological differences mention has already been made. Having 

 thus shown how the beds under consideration differ lithologically 

 and palaeontologicaUy from the beds composing the zone of Ammo- 

 nites BucMandi, I propose to notice shortly the Madreporaria of the 

 other strata of the so-called Lower Lias of Great Britain. 



5. Notice of the Madreporaria of other British strata of the horizon 

 of Brocastle and of the Ammonites -planorbis zone, ^-c. — ^Whilst inves- 

 tigating the Lias of the Isle of Skye, Dr. Wright found a coral-bed at 

 Lussayt, consisting of great blocks of a species which he has named 

 Isastrcea Murchisoni. Dr. "Wright considered this coral-bed to be 

 very low in the Liassic series, and, from the presence of Cardinia 

 co7icin?i«, Zieten, in the strata immediately beneath, he determined 



* Quart. Journ. Geol. Soc. Tol. xxii, p. 74. t Bid. vol. xiv. p. 35. 



VOL, XXm.— -PAKI I. c 



