378 ARRAN. GEOLOGY. SECONDARY STRATA. 



is found unusually hard and condensed. In many 

 places, it acquires that dark blue colour which so often 

 occurs where it is traversed by trap veins. The colour 

 of these beds, united to their erect position and compact 

 structure, has caused them to be mistaken for veins of 

 trap ; an error easily committed. This mistake may how- 

 ever be corrected by a close examination ; and it would 

 not have been noticed but for the purpose of cautioning 

 observers against judging in similar cases from any evi- 

 dence short of a careful manual investigation. One or 

 two narrow veins of this substance are nevertheless found 

 here in the bed of the river ; but they bear a small pro- 

 portion to the rock now described, while it is at the same 

 time very difficult to distinguish them among the rest. It 

 is probably owing to these veins that the sandstone has 

 here, as in other instances along the shore, assumed the 

 peculiar colour it exhibits. 



Near this spot, veins of sulphat of barytes are found. 

 These are numerous and of large size, traversing the 

 sandstone in different directions. They are for the most 

 part solid, and present the mineral only in its massive 

 form ; but some imperfect crystallizations have occa- 

 sionally been found in them. 



The proximity of the granite to the sandstone is here 

 such, that strong hopes are at first excited of being able 

 to trace their contact and ascertain their junction. They 

 can be distinctly followed till within 100 yards, or less, of 

 each other; not the least indication of the intervention 

 of schist appearing, either on the sides of the hills which 

 bound the river, or in its bed, or from the presence of 

 loose fragments. Unfortunately, the interval where the 

 contact might be expected, is so completely overwhelmed 

 by enormous loose blocks of granite, and the fixed rocks 

 are so concealed from view, that not a conjecture can be 

 formed respecting their nature. The research is equally 

 fruitless in the hills above; the deeply covered nature 

 of the ground, and the absence of streams sufficiently 



