52 Transactions of the 



The following list of fossils characteristic of the Rhiietic beds 

 is given in Jukes' Manual. 

 Concfdfera. — Avicula contorta, Cardium rhpeticuni, Modiola 



minima, Monotis (avicula) decussata, Ostrea liassica, Ostrea 



intusstriata, Pecten valonensis, Pullastra areuicola. 

 Crustacea. — Estheria minuta, var. Brodieaua. 

 Fish. — Acrodus acutus, A. minimus, Ceratodus altus, and five 



others, Hybodus minor and four others, Nemacanthus monilifer, 



Saurichthys apicalis. 



The teeth of a small mammal, supposed to be marsupial, and 

 called Microlestes antiquus, have been found near Frome, in a 

 fissure in the carboniferous limestone, the contents of which are 

 supposed to be of Rhsetic age. 



One of the most interesting features presented at Aust is the 

 display of no fewer than five nearly vertical faults in a cliff not 

 exceeding a quarter of a mile in length. The distinct character 

 and colours which belong to each of the strata, and the clear dis- 

 play of them which is afforded along the whole line of the section 

 by the vertical state of the cliff, render it a most eligible spot for 

 observing the phenomena of faults. In each case the right side 

 has fallen, when the supporting beds have given way or disappeared 

 from beneath. The first fault, where the cliff is lowest, is the 

 greatest, the fall being eighteen feet. The second is the best dis- 

 played of them all ; the fall is sixteen feet. The beds beneath 

 having sunk, and with them the cliff, a crack of some feet in width 

 is presented, whicli has become filled i;p with drift ; but down the 

 sides, between the drift and the rock of the cliff, a thick vein of 

 sulphate of strontian has run down. A thin vein also lines the first 

 fault. Each of the faults has acted like a dam to the rain water, 

 which percolates through the soil, and drains over the inclined 

 plain of the strata, giving rise to a spring which deposits a thin 

 incrustation upon the cliff, saving it in this way from rapid 

 destruction. The Severn continually washes away the base of 

 the cliff, which is now quite hidden by rubbish brought away by 

 the waters. 



It now remains to describe the fossils found in the cliff, 

 which are obtained in great profusion. Among the shells the 

 Ostrea liassica is a small oyster. 



The Plagiostoma giganteum is a common liassic bivalve, as 

 well as P. striatum ; Pecten valonensis is characteristic of these 

 beds. 



The Modioli are small at Aust ; they are also bivalves. 



Fossil fish-scales are very valuable, though not rare, on account 

 of the facility they afford of determining the classes of fish. Those 

 of the Mesozoic epoch are totally different from living species, and 



