82 



CHAPTER VIL 



ON INTERMEDIATE OR TRANSITION ROCKS. 



Characters and Classification of Transition Rocks. — Slate or Clay-Slate. — Pecul- 

 iarities of Structure. — Varieties of Slate. — Flinty Slate. — Greywacke andGrey- 

 wacke-Slate ; its Passage into Red Sandstone and Gritstone. — Errors of Geolo- 

 gists respecting the old Red Sandstone. — Lower Transition-Limestone: re- 

 markable Position of its Beds. — Upper Transition or Mountain Limestone. — 

 Magnesian Limestone, in Mountain Limestone. — Peculiarities in the Stratifi- 

 cation of Clouds Hill. — Errors respecting the Mountain Limestone of Derby- 

 shire. — Remarkable Structure of Crich Cliti'. — Cluartz Rock. — Jasper Green- 

 stone. — Coal Strata in England separate the Upper Transition Rocks from the 

 Secondary. — Observations on the Transition Rocks of distant Countries, — Er- 

 rors of Geologists respecting them. 



Transition or intermediate rocks cover rocks of the primary class, 

 and are distinguished as the lowest rocks in which the fossil remains 

 of animals or vegetables are found ; they may be regarded as the 

 most ancient records of our globe, imprinted with the natural history 

 of its earliest inhabitants. 



Transition rocks are the principal repositories of metallic ores, 

 which occur (both in veins and beds) more abundantly in many of 

 the rocks of this class than in primary rocks. Metallic veins very 

 rarely occur in the secondary strata. 



Geologists have often been perplexed, in their attempts to draw a 

 well-marked line of distinction between primary and transition rocks: 

 the difficulty has arisen, chiefly, from their arranging slate with the 

 primary class ; and hence the disciples of Werner have been obli- 

 ged to introduce the theoretical terms of newer and older primary 

 slate, and newer and older transition slate, he. If the occurrence 

 of organic remains in rocks be the characteristic distinction between 

 the primary and transition class, slate must certainly be classed with 

 the latter ; for it is among the slate rocks that the fossilized remains 

 of animals and vegetables first appear, in every country that has yet 

 been examined. One of the disciples of Werner, M. D'Aubuisson, 

 admits that there is no where any extensive formation of primary 

 slate. M. Bonnard, another disciple of the same school, in his 

 jpergu Geognostique des Terrains, after enumerating various prima- 

 ry slate rocks, candidly acknowledges, that it is doubtful whether pri- 

 mary slate can any where be found. It is true, that mica-slate pass- 

 es, by almost imperceptible gradations, into common slate ; but here, 

 as in other instances, we only find that Nature is not limited by the 

 artificial arrangements of the geologist : yet, so long as it may be 

 proper to class rocks containing organic remains with transition rocks, 

 we must place slate among them. Nor can this be invalidated by 

 the fact, that in some slate rocks no vestiges of animal or vegetable 



