522 ON THE SO-CALLED " UPPER-LIAS CLAY " OF DOWN CLIFFS. 



read lists in support of this view, showing that forms identified as 

 A. radians and A. striatalus occur with the ordinary characteristic 

 species in the basement-beds of the Upper Lias, as far as Lincoln- 

 sliire. Hence, while accepting the Author's facts, he could not 

 accept his conclusions, as by so doing we should abolish the Upper 

 Lias throughout the country. 



The occurrence of ^. opalinus y^'ith. A. Murchisonw was interesting. 

 Such an association of two zonal forms was common in the Lias, in 

 the case of A. margaritatus and A. sjnnatiis, &c. He pointed out 

 that the Author appeared to settle his zone in defiance of strati- 

 graphical evidence, by range of species rather than by the assem- 

 blages of forms, upon which he (the speaker) would himself prefer 

 to lay stress. 



Mr. Htjdleston pointed out that we had here a test case as to the 

 relative value of lithological and palaeontological characters in deter- 

 mining horizons. At Down Clifis he thought the Anthor was practi- 

 cally correct in his contention that the clays were a continuation of 

 the Yeovil Sands w^ith Ammonites of the upper part of the Jurense- 

 zone. He had very little doubt that, in the main, the Author's 

 Ammonite-horizons were accurate; and that, when a predominance 

 of any particular Ammonite occurred, it indicated a definite horizon, 

 whatsoever might be the lithological characters of the horizon. He 

 was surprised at Mr. Woodward's remarks concerning the comming- 

 ling of forms in the Marlstone, including species usually characteristic 

 of the Jiirense-zone. He could not understand this, and laid great 

 stress on the desirability of collecting fossils inch by inch, as other- 

 wise zones might easily be missed. He felt that the statement that 

 such forms as Amm. margaritatus, spinatus, bifrons, comma nis, and 

 radians occurred together should be challenged ; for if they did, the 

 whole question of the identification of strata by organic remains was 

 attended with extreme difficulty. He, however, objected to the 

 introduction of the term " Toarcian " in the sense used by the Author ; 

 for English geologists were the best judges of what were the proper 

 divisions of their own Jurassic rocks, and M. de Lapparent was 

 on the side of the British geologists so far as to include the 

 "Maliere" of Normandy (zone of Amm. Mtirchisona' and ajjalioius) 

 in the Bajocian. On purely palaeontological grounds he thought 

 the best line between Upper Lias and Inferior Oolite was tlie base 

 of the Opalinus-zone. 



Mr. H. B. WooDAVAED did not wish to assert that the forms 

 identified as Amm. radians and A. striatidus were common in the 

 Marlstone or Upper Lias. 



The President thought that there was a tendency to aim at a 

 too artificial precision of palaeontological zones, and to regard these 

 as everywhere applicable. He believed that in Nature there were 

 no hard-and-fast lines, either lithological or pahcontological. As 

 regards tracing lines for cartographical purposes, he did not know 

 how this could be done Avithout some lithological characters upon 

 which to dci)end, and he would be very sorry to sec the lino which 

 Mr. Woodward had drawn done away with. 



