Mr. Hen slow’s Supplementary Observations , &c. 483 
The knowledge of the few additional facts that I now offer 
may tend to promote further enquiry into the structure of this 
Island ; but much yet remains to be done before a complete account 
can be expected. 
Dr. Berger himself admits his map to be faulty, and I was 
entirely destitute of the means of accurately correcting it ; but some 
of the positions are so erroneously laid down as materially to affect 
what I have to communicate, and I therefore, submit to the Society 
a rough sketch of the mountains (Plate 35), particularly of the 
central chain, which will, I hope, serve to convey at least a general 
idea of their disposition. The chief error in Dr. Berger’s map is 
in the delineation of the southern group, the whole of which has 
been brought three or four miles too much to the east ; by which 
means the road from Castletown to St. John’s is thrown on the 
west, instead of the opposite side of South Barrule. Cronknyirrea- 
Lhaa also, as well as the mountainous ground stretching from it to 
Brada head, is made to rise about midway between the east and 
west coasts, instead of forming an overhanging cliff to the latter. 
A central chain may be distinctly traced from north Barrule to 
Cronknyirrea-Lhaa, bearing north-east and south-west, a direction 
nearly parallel to the greatest length of the island. This chain 
includes most of the highest mountains, the tops of which are 
nearly in the same straight line, with the exception of Cronknyirrea- 
Lhaa, which lying rather to the north of this direction, gives the 
southern extremity a slight curvature towards the west. 
As cursory observations require no particular method of arrange- 
ment, I shall follow that adopted by Dr. Berger, beginning with 
granite and gneiss. 
Granite exists in much ^greater quantity in the Isle of Man, than 
appears to have been suspected by Dr. Berger, and may be traced 
