part 4] 



PLIOCENE DEPOSITS OF CORNWALL. 



371 



was made, and with entirely satisfactory results. In figs. 2-4 

 from drawings of species occurring in St.' Erth, St. A.gnes, and 

 North- Western Wiltshire, it will be seen that there is a marked 

 similarity in crystal form in all cases; this is supplemented by a 

 careful comparison of all the kyanite-grains in the Seend residue 

 with those in the Cornish deposits. On the whole, the Pliocene 

 grains are more worn and rounded than those of the Lower G-reen- 

 sand, as Ave should expect ; but the species from Seend show the 



Fig. 



-Kyanite from Pliocene, 

 St. Erth (x?0). 



Fig. 3. — Kyanite from I*lio- 

 cene, St. Agnes ( X 70). 



Fig. 4. — Kyanite from Aptian, Seend, Wiltshire ( x 70). 



same characteristic prisms terminated by (001) or basal parting, 

 further individualized by cleavage-traces parallel to (010) and 

 (001), as well as the short ' stumpy ' varieties met with in the 

 Pliocene deposits. This mineralogical similarity seems, at first, to 

 be but slender evidence on which to found a source of origin for 

 the kyanite occurring in the Cornish deposits ; but, when certain 

 other factors are taken into account, it soon becomes apparent that 

 this north-eastern region was indeed the most probable source of 

 supply. 



