400 REV. THOMAS BROWN ON THE MOUNTAIN LIMESTONE AND 
struther to Pittenweem), are exactly those in which the shell-beds are least pre- 
valent. One is struck further also with the immense extent to which the ocean 
of that early time must have been pervaded by this form of life, its waters swarm- 
ing with myriads of these bi-valves. It can hardly have been a shallow sea, 
across the bottom of which there stretched continuously layers of dead shells 
four or five feet in thickness, more especially when we observe that just in pro- 
portion as the accompanying beds abound in evidences of marine conditions, 
these bands of Myalina are the more fully developed. 
Among these lower rocks may be noticed the occurrence near Caiplie of what 
is termed in the neighbourhood the petrified forest, a thick bed of sandstone with - 
twelve or fifteen trunks of trees, some of them prostrate, but most showing their 
stumps projecting through the rock. As the bed dips at about fifteen degrees to 
the east, and the trees lie slanting at about seventy-five degrees west, they are 
nearly perpendicular to the plane of the bed, showing that they must have been 
growing on the spot when enveloped in the sand. Unlike those of Craigleith 
there is no real petrifaction ; they are simply casts of the inside of the stem from 
which the bark has subsequently fallen away, but which show obscurely the flut- 
ings and other marks peculiar to the genus Sigillaria. 
Another circumstance of great importance to the understanding of this lower 
series is, that at various levels it shows beds with unequivocal marine fossils. 
Thus there is a stratum with many specimens of Natica in the Billow Ness, and 
across near Caiplie it is again found with the same pretty little shell still better — 
preserved. Again, in the axis of the anti-clinal, near Fife Ness, there occur, along 
with some fish remains, species of Orthoceras, Chemnitzia, and Natica, the two last 
very beautifully preserved. South-east of Cambo is a bed charged with shells, — 
distinctly marine, and on the other side what appears to be the same stratum, 
more fully developed. A species of Schizodus especially, as formerly stated, is — 
found in great profusion. In the neighbourhood of Caiplie also there is a shale- 
bed with specimens of Lingula, on a different level from that in which the Natica 
prevails. 
Shells—Two species may be mentioned, both carboniferous, but different from 
those already referred to: 
Murchisonia trilineata, from near Cambo. 
Lingula marginata, near Caiplie. 
Along with these occurred Orthoceras cylindraceus, and Aviculopecten arenosa. 
These all comparatively lie deep in the series. 
One of the most interesting discoveries which I met with in this lower series 
is a thin stratum of reddish limestone, charged in great abundance with a little 
Annelid, a species of Spirorbis or Serpula. It is allied to the Spirorbis (Micro-_ 
conchus) carbonarius, but larger in size, and, instead of being folded on itself like 
the coil of an Ammonite, is remarkably twisted in a serpentine form. 

