INTRODUCTION. XXXill 
which in many places are not only numerous, but in almost perfect parallelism to one 
another), it is impossible to take a single safe step in determining the successive groups 
of the Cambrian series. 
Several facts connected with this subject were established by myself in 1822, after 
much hard labour, and a multitude of careful sections made among the Cumbrian moun- 
tains: viz. (1) That the strike of the cleavage-planes, when they were well-developed, and 
passed through well-defined mountain-ridges, was nearly coincident with the strike of 
the beds. (2) That the dip of these planes (whether in quantity or direction) was not 
regulated by the dip of the beds; inasmuch as the cleavage-planes would often remain 
unchanged while they passed through beds that changed their prevailing dip, or were 
contorted. (3) That where the features of the country, and the strike of the beds, were 
ill defined, the strike of the cleavage-planes became also ill defined, so as sometimes to 
be inclined to the strike of the beds at a considerable angle. (4) Lastly, that in all 
cases where the cleavage-planes were well developed, among the finer slate-rocks, they had 
produced a new arrangement of the minutest particles of the beds through which they passed. 
As a general conclusion from these facts, it seemed to follow, that the cleavage-planes 
were the result of a crystalline, and not of a merely mechanical action. This latter con- 
clusion seemed to be sanctioned by a series of facts, of a kind both positive and negative. 
Thus I found examples of old strata, where the cleavage-planes occasionally disappeared, 
and again within a short distance reappeared, on a sudden modification of the mineral 
constituents.—Such, for example, as a change in the proportion of carbonate of lime, 
which seems in many cases to have facilitated the formation of cleavage-planes. 
I will take a more definite. example, from the calcareous slates and the limestone 
of Coniston. Generally, the calcareous slates and the limestone range together; the former 
shewing transverse cleavage-planes in great perfection; the latter very little affected by 
them: but at the south-western extremity of their range (not far from the coast of Cum- 
berland) the calcareous matter of the slates becomes superabundant, the fissile structure 
partly disappears, and the whole mass puts on a globular structure—being to a considerable 
extent made up of spherical calcareous concretions, some of which are two or three inches 
in diameter. But how are these concretions arranged? Not parallel to the true beds, as 
might have been expected; but parallel to the cleavage-planes of the ordinary calcareous 
slates. The case admits of no doubt; for the globular and fissile structures pass, almost 
insensibly, one into the other along the line of strike; as may be clearly seen in a succes- 
sion of open quarries. That the several spheres have been formed by a crystalline action 
round a fixed center no one will perhaps doubt. But this action has been accompanied by 
another, and a more general action, which has modified the position of the spheres, and 
has coincided in direction with that power which, under other mineral conditions, produced 
the cleavage-planes. It may not be easy to explain such complicated phenomena; but it is, 
I think, obvious that they are utterly out of the reach of any merely mechanical agency, 
in whatever way applied. 
