212 SIR ROBERT CHRISTISON, BART., ON FOSSIL TREES 
scale by cutting across the entire trunk of No. 6, nearly 3 feet in diameter, and 
polishing the whole surfaces. The first trial failed to show concentric layers. 
A second section, of which one side is preserved in the Botanic Garden 
Museum, and the other in the Museum of Science and Art, shows in many 
places long stretches of rudely parallel concentric layers, rendered distinct by 
fine lines of white crystalline matter formed at the junction of the annual layers, 
while the boundaries of others are faintly marked by characters to be noticed 
in now describing the structure of No. 7. 
This fragment, wherever it is stripped of its coaly crust, is finely fibrous on 
the surface, like that of wood. It is extremely tough. It has a dull grey 
colour, which, when it is polished, becomes shining black, like the finest black 
marble. A cross section, near its wider end, is of the shape of the letter D. 
On its polished surface may be seen in some lights nine faint marks, in some- 
what parallel concentric curves, crossing from the straight line of the D to the 
opposite curved side, but interrupted by white calcareous veins. A thin trans- 
verse slice 24 inches long, and 1% inch 
wide, taken from the straight side where 
these marks were most distinct, and in- 
cluding five of them, shows by transmitted 
light to the naked eye, and still better 
before a common magnifier of three or 
four powers, that the marks are really 
the boundaries of annual rings, varying 
Transverse Section of probably the portion of a from yoth of an inch to 3 an inch in width, 
branch of Fossilised’ Wood from, Craigleith Rows of ‘parallel cells “and transverse 
Quarry. Natural size. Showing the Annual é 
Layers of Wood.* medullary rays are seen crossing the sur- 
face, forming at each of the boundaries an 
open loop, always in one direction, and presenting a darker and a lighter shade 
on the opposite sides of the loop, so that the boundaries have much the appear- 
ance of a mountain chain as usually represented on amap. As the curvature of 
these boundary lines is very small, it is evident that they must have formed 
part of large circles. The fragment, therefore, is the longitudinally split 
segment either of a trunk or of a large branch. The only place where it is 
possible that bark had once existed is at the convexity, towards which 
alone the lines are convex. Nevertheless the whole circumference of the 
seement had been uniformly covered with the crust of bituminous coal. Hence 
this crust cannot have been bark. 
The structure of Nos. 6 and’7, as now described, agrees in all respects with 

* Mr Nichol, in his papers in the Edin. New Phil. Journal for 1834 on the “ Structure of Vege- 
table Fossils,” says he found that two Araucarias which now exist have no annual rings; and two 
others indistinct rings. Numerous sections of A. imbricata and A. excelsa in the Botanic Garden 
Museum show the annual rings most distinctly. 

