104 Dr. Mac CuUoch on the 



present, is almost invariably marked by an uniformly undulatinj^ 

 insipid outline. Yet, when once examined, it is easily recog- 

 nised, even at a distance, by the peculiar aspect of the surface 

 which it occupies. Being unfavourable to the production of 

 peat, and mouldering with difficulty into soil, it is free from 

 that dense coating of the former substance, which covers al- 

 most all the rocks of Shetland to such a depth as to render the 

 examination of the interior country a matter of great difficulty, 

 and, not seldom, of considerable uncertainty. For this reason, 

 it protrudes every where through the soil ; resembling very 

 strongly in its effect, that appearance which is produced by 

 scattered blocks of granite. At the same time, the intervals 

 are distinguished by the greenness, no less than by the good- 

 ness of the pasture which they afford ; a circumstance always 

 attracting the attention of a geologist in this black and desolate 

 region, as it is rarely found in the interior country, or at a dis- 

 tance from the influence of the sea, unless where limestone or 

 serpentine are the substrata. 



Balta, almost alone, affords an opportunity of remarking the 

 character of the rock when broken into cliffs, and exhibiting a 

 considerable extent of bare surface. The greater part of the 

 east side of this island is precipitous, in some places exceeding 

 eighty feet in height. These cliffs are peculiarly rugged, and 

 quite unlike in their appearance to any with which I am ac- 

 quainted ; presenting no marks of stratification, nor of the sur- 

 face of beds ; and, at the same time, differing from any similar 

 precipices of granite, or of trap, on the different coasts of 

 Scotland, which I have examined. They are broken into in- 

 numerable angular small parts, by fissures in every possible di- 

 rection ; and it will hereafter be seen that this peculiarity arises 

 from a circumstance in the constitution of this rock which also 

 obscures its stratified structure and disposition. 



This obscurity of stratification in the diallage rock of Shet- 

 land is so considerable, that it would not be difficult, from 

 limited observations, to fall into the error of considering it as 

 an unstratified rock, and as analogous in its nature to granite. 

 More extensive and careful observations will leave no doubt re- 

 specting its stratified disposition. In examining the surface of 



