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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- 

 minag, 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 formationa If it be said that 

 these slates may owe their laminated texture to extremely minute 

 flakes of talc, 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 laminae, 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 maybe 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 phsenomena, 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 fossihferous 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 



