various parts of Ecotlatid. 44 1 



■with sets of concentric circles, consisting of fine black lines most 

 mathematically drawn, with their intervals often filled up by por- 

 tions of parallel circular segments, an appearance .similar to that 

 produced on the surface of some of the agates imbedded in trap, 

 and which on that account are called ocular. These black lines 

 are perfectly superficial. 



Cr'inan. 



The land about this harbour is remarkably disposed in small 

 elevated hillocks, producing an irregularity of aspect similar to that 

 of the Oban shore. The mode adopted in making the canal, by 

 cutting away the edges of these hills, so as to form a continuous 

 embankment against them for a considerable space, has brought 

 their structure to light, and given great facility to the investigation 

 of their composition. They are formed of a continued alternation 

 of beds, elevated to an angle of 80° or upwards, and in a general 

 view appearing to be nearly vertical. On examining these beds, 

 they are perceived to consist of the following substances. 



1 . Coarse gray wacke, very well characterized, and precisely cor- 

 responding to the definition, inasmuch as it consists of grains of 

 quartz cemented by clay slate. 



2. The same rock, in which grains of felspar as well as of quartz 

 are cemented by clay slate. 



3. Coarse grained graywacke of a slaty fracture, or graywacke 

 slate. 



4. A similar rock of a much finer texture. 



5. A perfectly homogeneous clay slate, not to be distinguished 

 from the finest varieties of the primitive sort. 



6. A similar slate of a pale greenish gray colour, and silky lustre, 

 approaching in character to chlorite slate. 



Vol. II. 3 k 



