160 



CRATERIFORM DISPOSITION. 



observing various outcrops on the surface of the ground, a, 6, c, d 

 (Jig- 259), they have inferred the existence of as many different 



. Dislocation, causing a single bed to appear as several. 



beds, and consequently great wealth, when, in reality, it was only 

 one and the same bed dislocated and raised up to different levels 

 by successive faults. 



13. Crate'riform disposition. The known formation of Monte- 

 Nuovo, in explaining to us the uplifting of the beds seen in its 

 crate'riform cavity, leads us to attribute also to upheavals, the 

 epochs of which are unknown, the structure of several other hil- 

 locks of the same country, such as those of the solfata'ra of Puz- 

 zuoli, of Camboldi, of Astroni, &c., where the strata are all raised 

 towards the axis of the excavation found in the centre. In these 

 hillocks, the bottom of the cavity, particularly at Astroni (Jig. 200), 

 presents the point of a tra'chytic dome, which doubtlessly caused 

 the elevation of the surrounding beds of pumice tu'fa. These 

 crater hillocks at once explain all those of the Champs-Phlegreens, 

 which are full at the top, but all the strata of which are raised 

 around the axis (fig- 261) ; probably there would be found at their 



Fig. 260. Crate'riform disposition, with 

 a tra'chytic hillock in the centre. 



Fig. 261. Hillock with strata 

 raised towards the summit. 



Fig. 262. 



base some point of a cone which had not been uplifted with suffi- 

 cient force to crack the summit. When strata 

 are inclined in opposite directions (Jig. 261), 

 like the two sides of a roof, they form w T hat is 

 termed an anteclinal axis ; but when they dip 

 oppositely, it is termed a synclinal axis (fig. 262). 

 Similar circumstances are observed in many places, on a greater 

 scale. At Cantal and Monte-Dore, basa'ltic and tra'chytic beds, 

 ivhich could only have been deposited on a horizontal plane, are 

 found raised up around one or more centres, leaving towards their 



point of convergence a crate'riform. 

 basin of more or less extent, or 

 rising around a more or less pro- 

 jecting tra'chytic dome (fig. 268), 

 like the Peak of TenerifTe, above 



Fig. 26 i. Beds eleculrd around a 

 tra'chytic dome. 



the escarpments surrounding it. 



13. W -* is meant by an anteclinal axis? What is a synclinal 



