GEOLOGY OF THE BRISTOL COAL-FIELD^ 323 



Black Eock Quarry. It is so named from nearly all the beds being 

 very dark in colour, from the presence of bitumen, which sometimes 

 is so plentiful as to give an unpleasant odour to the limestone, 

 especially when rubbed, and sometimes is found as a liquid in 

 small cavities. The quarry is an extensive one, being 770 feet in 

 length, and nearly 300 feet in height. The dip of the beds varies 

 from 20° to 30° to the S.S.E. They are famous, both in this country 

 and elsewhere, for the remains of gigantic fishes that once swarmed 

 in the water of the old carboniferous ocean. Our Museum contains 

 a fine collection of typical specimens, the originals of many of the 

 figures in the large work of Agassiz on fossil fishes. The strata in 

 this quarry are extremely regular and uniform. At the top of the 

 eastern extremity is a singular deposit of cherty ironstone, which 

 appears to have been the result of decomposition. It is full of 

 vacuoles, as if caused by the escape of gases, but no trace of fossils 

 can be seen. 



[899]. — Encrinite heds. — These attain a thickness of 112 feet, 

 and constitute a very large part of the quarry. The stone is one 

 complete mass of the stems, arms and heads of these exquisitely 

 beautiful echinoderms, the sea lilies. The stone, when polished 

 shews the forms in the most perfect manner, and are very favourite 

 specimens and in great request for ornamental work. In the centre 

 of these Encrinital Beds is one in which the largest specimens of 

 Trilobites have been found. It is singular that in this one 

 layer there should have been so many, when they are absent in the 

 others. Nearly all the species of Encrinites yet found have been 

 noticed in this spot. 



Agathocrinus planus (Mill.) ; Biclwcrinus radiatus (Aust.) ; 

 Poteriocrinus conicus (PhilL), crassus (Mill.), isacobus (Aust.), 

 pUcatus (Aust.), pentangularis {Wi)!.), tenuis (Mill, ),rostratus (Aust.), 

 JRhodocrinus costatus (Aust.) ; gratiulatus (Aust.), verus (Mill.) j 

 Platycrinus granulatus (Mill.), levis (Mill.), rugosus (Mill.), striatus 

 (Mill.), trigintidactylus (Aust.); Actinocrinus triacontadactylus (Aust.) 



15 — [961]. — Fish beds. — At this spot are three beds, so 

 remarkably uniform in thickness and parallelism as to be strikingly 



