f, EXPLANATION OF THE PLATES. 



Plate ]8. Sketch of the ground explanatory of the several appearances described 

 in the paper. The cross lines refer to the sections in Plate 21. The upper 

 part represents such profiles of the li?ies as seemed most necessary for the 

 elucidation of the subject. 



Plate 19. A Map, >vhich serres to represent the several vallies that communicate 

 with Glen Uoy at the altitude of its lines. It also points out the communi- 

 cation which it would have with the sea were it now filled with water to 

 the level of its uppermost line, the colour indicating both. 



Plate 20. A Map, for the purpose of pointing- out on a larger scale the commu- 

 nications of Glen Roy with the vallies in its vicinity that bear !he marks of 

 the lines. 



Plate 21. Sections referred to in Plate 18. 



Plate 22. Ideal sections referring to tiie circumstances represented in Plate 19. 



PLATE 2S. 



Porphyritic veins traversing the schist of St. Agnes in Cornwall, described in 

 the Rev. J. J. Conybeare's paper, page 401. 



Fig. 1. Is a view of Cligga Point, the promontory of which is formed of granite 

 resting upon the schist. The vein of elvan is seen passing through tiie 

 schist dipping at a smaller angle than that of its stratification. 



Fig. 2 & 3. Are different examples of the veins of elvan in the schist, represent- 

 ing some of the irregularities that characterize them, 



PLATE 24. 



Appearance of the Paramoudra, and of oiner siliceous veins and nodules in 



chalk. 

 Fig. 1. Part of a vertical section of a chalk pic, near Moira, shewing in their 



relative proportions the chalk alternating with flinty nodules, with three 



specimens of Paramoudra; in their matrix. — (Scale half an inch to a foot). 

 Fig. 2. Specimen of a Paramoudra from the same place, presented by Dr. Bruce 



to the Museum at Oxford. 

 Fig. 3, 4, 5, 6. Other specimens seen in tlie same chalk pit near Moira. — 



(Scale of Nos. 2, 3, 4, 5, 6, an inch and a htilf to a foot.) 

 Fis.'. 7. Frao'ment broken from a Paramoudra iiiclosino- a small cluster of 



hexagonal cells, supposed to have been accidentally introduced from some 



extraneous body. (The drawing is magnified much beyond the natural size.) 

 Fig. 8. Veins of plated flint at Hurley Bottom, near Henley, cutting the beds 



of chalk and flinty nodules. (See Note, page 417.) 

 Fig. 9. Veins of flint cutting the chalk at Rottingdean, with strata of plated and 



nodular flints in the same section of the clifl'. — The lines represent strata 



and veins of plated flints. Tiie dots express siliceous nodules. (See Note, 



page 417.) 



