174 NOTES ON THE LIAS IN THE NEIGHB0T7BH00D OP KADSTOCB:. 



Grijpliea arcuata, fossils characteristic of the Bucklandi zone, and 

 with them we find Am. raricostatus, which is usually supposed to 

 be restricted to the top zone of the L. Lias. We shall see from 

 another section that bed (g) represents the Obtusus zone, so that 

 Am. raricostatus has passed through this. There is thus an over- 

 lapping of the Ammonite zones. The reason, apparently, is that 

 during the long period represented by the Bucklandi zone (which 

 includes over 100ft. of beds on the Glamorganshire coast) there 

 was in our district an extraordinary dearth of sediment, so that a 

 few feet of clay and limestone here represent a long period in 

 time, and the life conditions required by the fauna of the upper 

 zones of the L. Lias having come on during the interval, the latter 

 fauna appears commencing in the same bed in which the Am. 

 BucUandi was still a tenant. There really was not sufficient 

 sediment to be the burial ground of distinct zones of life. When 

 the climate, sea currents, or other conditions altered, the migra- 

 tion of fauna took place without there being any physical signs of 

 the lapse of time by the accumulation of detritus. That such a 

 lapse of time is here represented we have a right to infer from 

 finding in one bed Ammonites which generally occur in zones, 

 and separated by a considerable thickness of beds. It becomes 

 also plain that it is not the case here, as Mr. Moore has remarked, 

 that the greater part of the Bucklandi beds have been cut away, 

 or that the Obtusus zone has been cut away, and so on. We 

 maintain that they are all here, more or less, in the district, for 

 we have found most of the Ammonites which characterise these 

 zones in the L. Lias. 



The bed which comes above the clay is (g,) of a dark greenish 

 blue colour, with rather a laminated structure, at times, but the 

 heart of the bed is very tough. It contains Fish scales here, and is 

 the level of A. ohtusus and plamcostatus. Above this we have clay 

 (f 3,) with Belemnites penicillatus, Sow. ; then a bed of irregular 

 nodular grey limestone (f2), which divides the clay here, but 

 does not seem to be constant. In the clay above (fi) we have 

 found A. raricostatus, which is here in its proper place, and 



