244 NEW RED SANDSTONE. 



but the quarries in the White Lias are rarely opened deep enough 

 to expose it. Perhaps the best exposures of the stone are in the 

 railway-cuttings at Weston, and Kelston near Bath. (See Fig. 38.) 

 The irregular top of the Gotham Marble is not an eroded surface, 

 for thin layers may often be split off, which correspond to the 

 irregularities ; the same kind of uneven concretionary surface, on a 

 larger scale, may often be seen on the limestones of the Lower 

 Lias, a structure perhaps induced during the consolidation of the 

 beds. This concretionary and sometimes botryoidal surface is not 

 uncommon in the lowermost Purbeck Beds. The dendritic or 

 arborescent markings in the Gotham Marble were probably pro- 

 duced by infiltration of ores of manganese and iron in the soft 

 calcareous mud from which the rock originated. A thin bed of 

 limestone, showing imperfect dendritic markings, occurs also in 

 the lower Purbeck Beds of Durlston Bay, Swanage and other 

 localities. 



Occasionally the upper surface of the Sun Bed or Jew Stone presents a striated 

 appearance, being crossed in various directions by fine grooves. In some cases 

 these appearances are produced by weathering along lines of minute joints, and in 

 other cases they may be due to sun-cracks, modified subsequently by the erosive 

 action of water. ^ Sun-cracks, ripple-marks, pseudomorphous crystals of rock-salt, 

 sands, and conglomerates, occur at various horizons in the Rhpetic Beds, telling of 

 shallow water and of pauses in deposition. Perforations are occasionally met 

 with in the upper beds of the White Lias, which have been referred to the action 

 of boring Molluscs and Annelides. Specimens showing tubular perforations, 

 extending from two to nearly six inches into the stone, were obtained by Mr. 

 Bristow and Mr. Etheridge, from the White Lias at Curry Rivell, near Taunton ; 

 these perforations were probably the burrows of some marine animal in the soft 

 calcareous mud of the period." 



The White Lias, which is well developed in Devonshire and 

 Somersetshire, is poorly represented at Penarth, between Bristol 

 and Gloucester, in the ]\Iidland Gounties, and further to the north. 



The fossils of the White Lias include Modiola minima, Cardiuvi 

 Rhccticum, Ostrea Liassica, Plicatula intusstriata, Lima pnrcurso}', 

 Monotis decussata, Placunopsis alpina, Myophoria posiera (a form allied 

 to Trigonia'), Pkuromya \Ptcromya') Crocombeia, Schizodus (^Axim(s) 

 cloacinus, and other IMoUusca.^ An Esthcria-hQ(\ with Estheria 

 7ninuta, var. Brodicana, may sometimes be recognized in the lower 

 part of the White Lias. Cypn's Liassica also occurs ; as well as 

 Gorals of the genera JSIojitlivaltia and lliccosmilia. The fossils of 

 the White Lias are, as a rule, poorly preserved ; they are sometimes 

 abundant in the marly layers between the harder beds of stone. 

 Remains of Fishes and Insects are occasionally found in the 

 Gotham IMarble. 



Black Shahs. — These shales, which underlie the White Lias, 



1 See Rev. J. Sutcliffe, " A Short Litroduction to the Study of Geology," 181 7, 

 p. 21. 



= J. H. Blake and H. B. W., G. Mag. 1872, p. 196. 



3 For figures of Rhcetic fossils, see Moore, Q.J. xvii. 516; and Etheridge, 

 Trans. Cardiff Nat. Soc. iii. For lists of species, see also Geol. E. Somerset, etc. 

 (Geol. Survey), p. 87, Wright, Q.J. xvi. 374, Brodie, "A History of the Fossil 

 Insects," 1845. 



