552 MULL. GEOLOGY. 



of those which were mentioned at the beginning of this 

 discussion as having occurred between distant barometers. 

 It is evidently impossible to give any scale for the cor- 

 rection of this class of errors, as the data are unassignable. 

 But it remains certain, that the greater discrepances de- 

 pend on causes in the nature and movements of the atmo- 

 sphere, modified only by the minor errors of another class 

 arising from construction. Although the former should 

 never be discovered, nor the latter ever removed, this 

 slight sketch will have its use, by exciting such a salu- 

 tary distrust in barometric observations as will lead to 

 the use of all the precautions in our power towards 

 diminishing their inaccuracies. 



UNDER the circumstances of a rainy climate which have 

 already been mentioned, and in a country so constituted, we 

 should expect to meet with abundance of streams. Such 

 is in fact the case ; but the interstices among the hills are 

 so numerous, and the proximity of the shores to all 

 parts of the interior is such, as to allow of no considerable 

 accumulations of water. In the season of rain there may 

 be torrents, but the streams of Mull are, when moderate, 

 mere brooks. There is no one large enough to merit 

 a particular description. There is consequently no mate- 

 rial waste of land nor any considerable deposit of alluvium 

 to be traced to this cause, since the plains at Scallasdale 

 and in other places are of trifling extent ; nor do there 

 seem to exist either the accumulations of alluvia or the 

 detached and insulated stones which mark the operations 

 of a more distant and general cause. I shall now proceed 

 to a particular detail of the several rocks which enter 

 into the composition of this island. 



In describing a country so complicated both in form 

 and in structure as Mull, it is so difficult to make the 

 geological coincide with the geographical arrangements, 

 and at the same time to avoid repetition and confusion, 



