190 ARGILLACEOUS SCHIST. 



in Scotland, in Jersey, and elsewhere; both varieties 

 being indifferently lowest, as in other cases where the 

 same rocks occur in more limited portions. In all 

 these examples, it is followed by the secondary strata; 

 nor do I know that, on the great scale, any other pri- 

 mary reck has been observed succeeding to it, although, 

 on the small, I have found every one of them. The al- 

 ternations which it then presents are numerous and in- 

 tricate; and the history of these will determine the na- 

 ture of the rocks which it follows and precedes, as that 

 will show that it has no fixed place in the system, con- 

 sidered as a mere rock. That its larger masses may 

 follow any primary stratum, and thus also be still the 

 uppermost, it is superfluous to say. 



A remarkable example of its alternations, is the com- 

 pound series which terminates the Highlands to the 

 southward, and is followed by the lowest red sandstone; 

 misrepresented as a mere mass of clay-slate. The rocks 

 in question consist of different micaceons and chlorite 

 schists, with gray wackes equally various, clay-slate, and 

 limestone, and more rarely, with gneiss and hornblende 

 schist, irregularly intermingled, arid often presenting 

 transitions between several of the members; as from 

 the micaceous to the chlorite schist, and from the latter, 

 into gray wackes or clay-slate. Yet more or fewer of 

 those are found in different parts of this long and nar- 

 row deposit, which is sometimes reduced to the argil- 

 laceous schists alone : the whole graduating into the 

 micaceous schist which it succeeds, so that the limit is 

 scarcely ever definable. 



Its next remarkable association occurs in the chain 

 of Isla and Jura. Here, both the varieties alternate in 

 frequent repetitions with quartz rock and micaceous 

 schist ; the graywackes often passing into the conglo- 

 merates of the former ; while in some parts, the united 



