282 GEOLOGY OF THE BRISTOL COALFIELD. 



and lowest of the Liassic beds. The landscape stone, as the 

 Cotham marble is usually termed, is a smooth limestone having a 

 conchoidal fracture, and always permeated by numerous dendritic 

 markings of oxide of manganese with a small proportion of oxide of 

 iron. This curious bed of stone gradually thins out and disappears 

 about six miles to the north west of the city of Bristol, near to 

 Patchway station. 



The first beds of Lias with which w^e meet are those characterized 

 by the frequent occurrence of yEgoceras planorbis, and known 

 better by its old name of Ammonites planorbis. The planorbis 

 zone, as seen on Dundry Hill, attains a thickness of about 143 feet, 

 but probably the best place for examining the beds and collecting 

 the fossils is Watery Lane and on Ashley Down. In all these 

 locahties good specimens of planorbis may be obtained in great 

 numbers, and occasionally [in a perfect state of preservation. In 

 the quarries at Montpelier is a bed exactly at the base of the series, 

 and may at once be recognised by numerous examples of avicula 

 longicostata. The men generally speak of this as the "J)ottom led^^ 

 because no more limestone for burning is to be obtained. Mont- 

 peher is a capital locality for typical specimens of Ammonites 

 {^goceras) Johnstoni, so familiar to the visitors at Watchet. At 

 Cotham, in this position of the lias, most of the Sutton fossils are 

 to be obtained immediately below the Pholidophorus limestone- 

 Near the lime kiln at Montpelier are two beds of clay that are very 

 remarkable for the abundance of alveoli of Cidaris Edwardsi, with 

 foraminifera and entomostraca, altogether affording a charming 

 group for the microscopist. 



Above these interesting beds are those of the Bucklandi zone, 

 which attain 120 feet in thickness. But the best section for the 

 palaeontologist occurs at Horlield, Cotham, Ashley Down, and 

 Whitchurch. Some examples of Ammonites {Art'eiites) Bucklandi 

 and A. Conybeari are very large. At Ashley Down, Ammonites 

 {^goceras) tortile is very common with Limagigantea and Gryphea 

 incurva, so much so as to deserve the distinctive appellation of the 



