ARRAN. GEOLOGY. OVERLYING ROCKS. 401 



requisite, or, from the imperfection of the modes of 

 reference, practicable.* 



It has already been shown that the greater part of 

 the southern district presents indications proving that 

 it is formed of a basis of red sandstone, covered and 

 obscured in various places, and throughout the greater 

 part of its extent, by overlying masses of unstratified 

 rock. These consist principally of the several varieties 

 of felspar rock, a certain extent of trap being also 

 found associated with them. The causes already pointed 

 out, consisting in the nature of the soil and the shape 

 of the ground, which render it impossible to assign the 

 points where the sandstone appears at the surface, equally 

 prevent any accurate account of the places of the over- 

 lying rocks. In a general view they may be considered 

 as occupying all the higher parts of the land ; while 

 the sandstone, inferior to them, is only to be seen where 

 natural causes have eroded the beds of torrents; or 

 on the sides of hills where the surface has undergone 

 changes of its original form. I must refer to the map 

 for the only record which I can give of these rocks over 

 the principal part of their extent within the interior : 

 it is necessarily of the most general nature; since the 

 want of local names, no less than the geographical 



* As all the substances above described are associated by the com- 

 mon bond of connexion and transition, and by that of a common posi- 

 tion with respect to the stratified rocks, a common geological term 

 might here be adopted for the whole. But to accommodate as much 

 as possible this description to the prevailing practice, that of trap will 

 be applied to the greenstone, basalt, and amygdaloid ; although some of 

 the other division will occasionally and unavoidably be included under 

 it. For that division, the term of felspar rock will be adopted, which, 

 however objectionable, is convenient because it is indefinite. The 

 use of any of the ordinary terms for this purpose, such as claystone, 

 clinkstone, syenite, or porphyry, would be more objectionable, from 

 their definite meaning; while to name each individual variety in treating 

 of the general details, would lead to perplexity and tedious repetitions. 

 It will be sufficient to specify them in their most important situations. 



VOL. II. D D 



