Mr Anderson oft the Quartz District of Inverness. 91 



as a body of its size would have had at the distance of the 

 part of the picture which it covered. 



We have seen an analogous illusion when viewing the mo- 

 saic pavement of St Paul's from the inside of the cupola. The 

 lozenges had a certain apparent magnitude when seen alone, 

 which, of course, was small. When a person, however, pass- 

 ed over the pavement, our knowledge of his size furnished us 

 with a scale for measuring the real magnitude of the compart- 

 ments in the pavement, and they accordingly increased in 

 size, diminishing again when the person had passed from our 

 view. 



Art. XVI. — On the Quartz District in the Neighbourhood of 

 Inverness. (Concluded from Vol. III. page 218.) By 

 Geokgk Anderson, Esq. F. R. S. E., F. S. S. A. & Se- 

 cretary to the Northern Institution for the Promotion of 

 Science and Literature at Inverness. Communicated by 

 the Author. 



Not to interfere with the description of the characters of the 

 Quartz-Rock, which was given in the last number of this 

 Journal, I have reserved for this place a sketch of its geo- 

 graphical distribution, together, with a few other detached no- 

 tices, which may now be brought forward without injuring 

 the order of the previous details. 



If we were to describe on a map the space which the quartz 

 rock occupies, its lines of boundary would appear to almost 

 meet at a point. This is the eastern extremity of the depo- 

 sit ; the quartz-rock lying between the granite and the strati- 

 fied sandstone, and assuming a general form that may be just- 

 ly called wedge-shaped. Towards the west and north the 

 quartz rock is extended far and wide, and is variously blended 

 with strata of gneiss. It cannot be said to observe the general 

 bearing of our Scotch chains of mountains, and, indeed, 

 its course seems to be transverse rather than parallel to the 

 northeasterly direction of the great Caledonian Valley. The 

 line of junction between the quartz and the granite, which is 

 so precise and conspicuous in the rocks of Dun-Jardil, is lost 



