IN THE GAWILaHUR HILLS. 291 
Gawilghur it appears stratified, the summits of several ra- 
vines presenting a continued stratum of many thousand 
yards in length. 
The basalt frequently and suddenly changes into a 
wacke of all degrees of induration, and I may say of every 
variety of composition usually found among trap-rocks. It 
changes, 
3. Into a rock, which may be named indifferently No- 
dular Wacke or Nodular Basalt, composed of nuclei of 
basalt, usually of great specific gravity, surrounded by 
concentric layers of a loose earthy mass resembling wacke, 
but without cohesion, which, on a superficial view, conveys 
to the mind every idea of a fluid mass of earth, having in 
its descent from some higher spot involved in its course all 
the rounded masses it encountered, and subsequently be- 
came consolidated by drying. A very slight inspection is 
sufficient to detect the true cause of this appearance, which 
is owing to the facility of decomposition of the outer crustj^ 
depending on difference of structure and composition. In 
none of the conglomerates or pudding-stones do we observe 
any traces of this structure ; and as it is common to the 
most crystalline greenstone, porphyritic greenstone, and 
those rocks usually denominated syenitic, there can be little 
doubt that it is owing to the development of a peculiar con- 
cretionary structure by decomposition. 
In a small ravine, near the village of Saulminda, 2000 
feet above the sea, I saw basalt of a perfectly columnar 
structure, and vertical, closely connected with a columnar 
mass, formed of concentric lamella, enclosing a heavy and 
hard nucleus. Perhaps these last were the ends of columns 
lying in a horizontal position. 
Near this ravine I had also an opportunity of observing 
the gradual and perfect passage of the columnar basalt into 
that which has been called Stratified, from the parallelism 
T 9> 
