138 Mr Nicol on the Structure of 



half the distance, between the pith and the surface, there were 

 ten layers in an inch, and near the surface there were fifteen 

 layers in an inch. In a native tree of the same species, from the 

 same quarter, 160 years old, the diameter of which was exactly 

 the same as the other, the relative breadths of the layers were re- 

 markably different. The broadest layer in this tree exceeded 

 not the tenth of an inch ; whereas, in the other, the broadest 

 was nearly three tenths. From the pith to the distance of one 

 inch, there were twenty-six layers. From the age of 40 to 

 52 years namely, twelve layers occupied an inch. From the 

 age of 70 to 86 years namely, sixteen layers occupied an 

 inch ; from the age of 105 to that of 125 namely, twenty 

 layers occupied an inch ; from the age of 130 to that of 160 

 namely, thirty layers occupied an inch. From these measure- 

 ments it will appear that, throughout the whole semi-diame- 

 ter, the broadest layers of the native tree were scarcely double 

 the breadth of the narrowest ; whilst, in the planted tree, some of 

 the broadest layers were upwards of four times the breadth of 

 the narrowest. The diameter of these two trees being the same, 

 the growth of the native must have been slower and much more 

 uniform than that of the other ; and this uniformity of growth is, 

 in all probability, a principal cause of the well known superior 

 strength of the native pines in the Highlands of Scotland. On 

 observing the differences between these two trees, I was natu- 

 rally led to examine some other individuals of the same kinds, 

 and found the same conformation in the whole of them. 



A striking illustration of the superior strength of the native 

 Scotch firs occurred during the erection of a bridge, which, a few 

 years ago, was thrown over the river Don, in the vicinity of 

 Aberdeen. In consequence of the softness of the ground, it was 

 found necessary to build the bridge on piles thirty feet long. 

 Logs of the best Memel timber were first employed, but it was 

 soon found that their tenacity was insufficient to resist the force 

 necessary to drive them to the requisite depth, although their 

 upper extremities were strongly guarded with hoops of iron. 

 Recourse was then had to the native pines of the forests of 

 Braemar, and these withstood the utmost efforts of the driving 

 machine. 



I have stated that the annual layers are generally broader 



