No Fixed Sequence in Slate-Formaiions. 11 



and finally the grey wacke on the clay-slate. From single ob- 

 servations of this kind, a general rule ha& been laid down. 

 But the exceptions from this rule are just as numerous, if they 

 are not more numerous, than the cases conformable to it. In 

 order, however, to find a conformability to rule in this irregu- 

 lar alternation, and in order to deduce from it determinable 

 formations, not only have rocks, which, in another series, 

 would have been termed gneiss and clay-slate, been denomi- 

 nated grey wacke or grey wacke- slate, but it has been assumed 

 that to granite there succeeds first an alternation of granite 

 gneiss, then pure gneiss ; to it an alternation of gneiss and 

 mica-slate, then pure mica-slate, &c. But none of all the possi- 

 ble combinations of these, and, if regard were paid to the series 

 of beds included in them, none of the double or more compound 

 combinations of included beds amongst themselves or with 

 others, should be passed over, if the diversity of nature were 

 to be represented ; and it would then result from these that 

 this diversity includes all possible sequences, and that therefore 

 a certain determinate order, and one which is sought as a con- 

 sequence of a theory, cannot exist. 



Hardly any one can misapprehend the importance, in reference 

 to the search after, and discovery of, repositories of useful mi- 

 nerals, of the knowledge, that a fixed order in the superpo- 

 sition of the mountain-rocks, from which a fixed sequence had 

 been deduced, does not exist in what are termed the primitive 

 and transition series. For when, for example, we know that 

 in a certain district, the beds or veins, of which we are in pm-- 

 suit^ only occur in mica-slate, and not in the gneiss and clay- 

 slate, and we find the gneiss on the lying side, and the clay- 

 slate on the hanging side, of the rocky mass in which we have 

 hitherto instituted our investigations, we could not hope for a 

 fortunate result either beyond the former or the latter, if we 

 should adopt as correct the assumption of the invariable se- 

 quence of the rocks, and would hence perhaps consider as su- 

 perfluous the further investigation of the neighboiu:hood. But 

 mica-slate can make its appearance under the gneiss and above 

 the clay-slate. So long as we remain within the boundaries 

 of the slaty rocks, we may expect generally to meet with every 

 succession of the individual members, and must acquire a 



