390 DESCRIPTION OF THE COUNTRY BORDERING 



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a, a. Volcanic grit. b. Volcanic grit, amygdaloidal. c. Volcanic grit, with shales, d. Metamorphosed sandy shales, c. Metamor- 

 phosed sandstones. /. Metamorphosed sand-rock. 



The top rock (No. 76) is from eight to ten feet thick, and differs in colour, grain, 

 hardness, and compactness at different places. In some parts it abounds with 

 amygdules, and in others contains but few. It is separated from No. 77 by from 

 six to eight inches of thinly-laminated siliceous material. No. 77 is about ten feet 

 thick, and contains numerous amygdules and thin veins, containing calcite, zeolites, 

 thalite, and chlorite. It is jointed, and traversed by cracks in all directions. The 

 rock on the sides of the joints, from one to three inches in breadth, appears to be 

 more highly metamorphosed than in other parts ; caused, probably, by having been 

 long under the influence of ascending vapours, after other parts of the rock had 

 measurably cooled. 



The next rock (No. 78) is very soft in some places, and disintegrates easily, while 

 in others it is hard. In general, it is broken down with facility by the action of 

 the waves, and washes into caverns. It contains large nests filled with laumonite 

 and calcite. Where it is in near contact with trap rocks, it is traversed by veins of 

 argillaceous iron ore. Some of the layers are separated for long distances by seams 

 of laumonite. A portion of this rock, which is from five to twelve feet in thickness, 

 rests on a brecciated conglomerate, which contains, however, pebbles only of its own 

 kind. The breccia is only to be seen in the near vicinity of the trap. Nos. 79, 80, 

 81, 82, 83, were all taken from the same bed, at the same elevation, and within a 

 distance of six feet. These beds dip southeast at an angle of 11°. Eighty-five yards 

 further the dip is reversed, and the beds just described are overlaid by basalt (Nos. 

 84, 85), as shown in the section above. On the west side of the basaltic exposure, 

 near the junction of the breccia with it, are many nests containing green earth. 



The difference in the appearance of the same beds of rock, after having been sub- 

 jected to metamorphic influences, is owing, no doubt, to accidental variations in the 

 original constitution of the beds. The differences in the mineral contents of the 

 beds may, I think, be accounted for in the same way, taking into consideration the 

 particular metamorphosing agents, to the influence of which they have been sub- 

 jected. It may be set down as always the case, that minerals of a different cha- 

 racter from those found in the altered beds, are developed in the bedded traps, and 

 at the junction of dikes belonging to different systems. And it is also true, that 

 where the sedimentary rocks are overlaid by basaltic beds, the minerals are far 

 more abundant in the sedimentary beds than in the trap. The section on the next 

 page occurs a short distance above the one last given. 



The top layer here resembles very much the altered porphyritic shales of Wisa- 

 code River. 



About half a mile above this place, is a low exposure of metamorphosed rock, 

 overlaid by a bed of trap. The trap is in a broad sheet, from eighteen inches to two 



