EXPLANATION OF THE PLATES. 



PLATE XXX. 



Figs. 1 & 2. Two species of Orthocera, mentioned in page 204. 



The other figures in this plate represent the columns of circular discs men- 

 tioned in page 204 ; but it has not yet been ascertained to what class of fossils 

 they belong. 



PLATE XXXL 



Map of Lake Huron. 



For the authorities from which it is compiled, see p. 177 of this volume. 



PLATE XXXIL 



Fig. 1. represents a section passing from north-north-west to south-south-east, 

 through Blaze Castle, the Bristol coal basin, and Downhead upon Mendip. In 

 figures 1 A. 1 B. and 1 C, the line of section is partially changed. 



Fig. 2. represents a section passing from north to south through Tortworth, the 

 Bristol coal basin, and Lyal hill near Wells. In figures 2 A. and 2 B. the line 

 of section is partially changed. 



Fig. 3. represents a section passing nearly from north to south through Portishead, 

 the Nailsea coal field, and Cheddar. In figures 3 A. 3 B. 3 C, the line of section 

 is partially changed. 



Fig. 4. represents a section passing from west to east through Henbury, the Bristol 

 coal basin, and Wyck rocks near Bath. 



Fig. 5. represents a section passing from north-west to south-east through Little 

 Doward Hill, the coal basin of the Forest of Dean, and Blakeney Hill. 



PLATE XXXIII. 



Fig. 1. is a plan of the Clifton defile, from Rownham ferry to Hungroad. 



. 2. is a section of tl 

 Clifton to Sea-mills. 



Fig. 2. is a section of the strata on the north-eastern bank of the same defile, from 



PLATE XXXIV. 



Fig. 1. is an enlarged section of the southernmost part of the defile of Clifton, ex- 

 hibiting the great fault which traverses it to the north of St. Vincent's rocks. 



Fig. 2. represents a section passing north and south from Brecon to the Bristol 

 Channel across the coal basin of South VTales. 



Fig. 3. represents an enlarged section of the southernmost part of fig. 2. 



2b2 



