EXPLANATION OF THE PLATES. 



or cutting surface of the tooth is composed, — the curved and slightly convex form of 

 the anterior part of its body, — its flat side slightly depressed in the centre, and its 

 flat and somewhat concave posterior surface. The fractured lower part permits a 

 view of its square hollow cavity, which contained the vascular pyramidal pulp, on 

 and from which the tooth was continually growing and projected upwards, in pro- 

 portion as its grinding surface was worn away by attrition. 



Plate XLVI 



Two views of a small fragment of the shell or cuirass discovered at Las Averias, and de- 

 scribed at No. 3. Plate XLIIL, represented of the natural size. Although a con- 

 siderable number of pieces of this armour have been preserved, — as many, perhaps, 

 as would cover a space of five feet square, — it was difficult to select a portion suffi- 

 ciently perfect on both surfaces to show its structure satisfactorily. A great part of 

 this covering is incrusted on both surfaces by a very dense calcareous cement, the 

 removal of which always produced more or less injury to the fragile surface. In this 

 example, however, both surfaces are sufficiently perfect to show the relative size and 

 number of tesserae of which it is composed, and their forms, which are generally 

 irregular hexagons. They are united to each other by indented sutures. 



Fig. 1. The external surface. 



Fig. 2. The internal surface. 



PLATE XLVII. 



Sections in North Wales, distinguishing stratification from cleavage ; in illustration of 

 Prof. Sedgwick's memoir on the Structure of large mineral masses, p. 461. 



Fig. 1. Transverse section through a part of the great chain of North Wales, showing the 

 anticlinal lines. The cleavage planes are omitted: see p. ^TO. 



Fig. 2. Section through the western flank of the chain, as seen on the south side of the 

 great road about seven miles east of Bangor. The beds and cleavage planes are both 

 exhibited : see p. 475. 



Fig. 3. Section near Harlech ; (a) beds, (b) cleavage planes : p. 475. 



Fig. 4 and 4 a. Contorted strata on the left bank of the Towey : pp. 470, 475. 



Fig. 5. represents the position of the beds and cleavage planes in a section on the banks 

 of the Wye, a few miles above Rhaiadr : p. 476. 



Fig. 6. Arched beds in the slate quarry called Craig y Grebbin, on the road from Llan- 

 gollen to Ruthin : p. 476. 



Fig. 7. Section of calcareous slate rock, with subordinate beds of impure limestone, on 

 the west side of Foel Faur, about two miles from Llanrhaiadr: p. 476. 



Fig. 8. Profile of a ridge a few miles south-east of Bala. The lines represent the cleavage 

 planes; and the dots the stripes in the slate : p. 477. 



