316 Geological Society. 
in the Swiss Alps that the fissile roofing-slate and drawing-slate of 
the Niesen, in the Canton of Berne, divides into extremely thin la- 
minz, which are parallel to the true planes of stratification. The 
direction of the beds is shown by alternations of coarse and clearly 
mechanical strata of a kind of greywacke, the whole series belong- 
ing to the Green Sand or fucoid grit formation. Ifit be said that 
these slates may owe their laminated texture to extremely minute 
flakes of tale, mica, or some other foliated mineral which may have 
fallen as sediment and have been all deposited on their flat surfaces, 
I reply, that in that case they would exemplify the exact similarity 
of certain acknowledged slates of deposition to others which have 
originated in crystalline forces independent of sedimentary action. 
Mr. Murchison, after confirming the truth of the Professor’s obser- 
vations as applied to all those regions of Wales which have come 
within his survey, has pointed out what might by some be considered 
an exception to the rule in a part of the slate-rocks of Pembroke- 
shire, where the planes of slaty cleavage are coincident with the 
true lamin, as proved by colour and the alternation of various 
layers of deposit. Mr. Murchison states, however, that although 
these rocks are quarried as roofing-slates, and are a part of the older 
system, they may be classed by Mr. Sedgwick as fine flagstones. 
Some confusion will, I fear, arise from attempting to restrict the 
term slate to those cases alone where the cleavage is oblique to the 
stratification ; but whatever nomenclature we adopt, it is clear from 
the excellent paper of the Professor, that three distinct forms of 
structure are exhibited in certain rocks throughout large districts : 
namely, first, stratification ; secondly, joints; and thirdly, slaty 
cleavage; the last having no connexion with true bedding, and 
being superinduced by a cause absolutely independent of gravita- 
tion. These different structures must have different names, even 
though there may be cases, and I believe there will be many, where 
it is impossible, after carefully studying the phaenomena, to decide 
upon the class to which they belong. 
One curious consequence, but slightly alluded to by the author, ap- 
pears to follow from the facts described, namely, that the slaty struc- 
ture must have commenced at a period posterior to the last series of 
violent movements which dislocated the strata and threw them into 
anticlinal and synclinal lines. Such disturbances would have de- 
ranged the parallelism of the cleavage planes. If, therefore, there 
are proofs, as I believe there are, of the elevation or subsidence of 
these rocks since they assumed the slaty structure, the whole 
country must have been moved bodily, or the separate masses, 
if they changed their relative position, must have moved in such 
directions as to allow the dip of the cleavage planes to remain un- 
altered. 
It is with pleasure that I next call your attention to the investi- 
gations which Mr. Murchison has been steadily pursuing in the 
older fossiliferous rocks of Wales and the bordering counties of 
England. He has at length brought his survey of five years to a 
successful termination; and his work will form a most important 
