Graywacke. 249 



gists have given the term a much wider range. " It designates, 

 when taken in a more general sense," says Humboldt,* " every con- 

 glomerate, sandstone, and fragmentary or arenaceous rock of transi- 

 tion formation, that is anterior to the red sandstone and coal forma- 

 tion." " Viewed on the large scale," says De la Beche,f "the gray- 

 wacke series consists of a large stratified mass of arenaceous and 

 slaty rocks, intermingled with patches of limestone, which are often 

 continuous for considerable distances." I use the term in " the gen- 

 eral sense " described by Humboldt ; and include in it, both the * gray- 

 wacke group,' and ' the lowest fossiliferous group,' of De la Beche ; 

 though I am not sure that our series embraces any limestone. And 

 since the red sandstone does not occur in the eastern part of the 

 State, nor any other secondary rock, I am not sure that the series 

 under consideration, ought to be regarded as rilling up the whole 

 space between the red sandstone and the primary rocks. But every 

 geologist who examines this series, sees at once that some members 

 of it must belong to the oldest of those rocks which some writers de- 

 denominate transition. For the lower beds pass insensibly into pri- 

 mary rocks ; and generally, a chemical agency is obvious in their 

 structure, in the veins of quartz by which they are frequently trav- 

 ersed, and in their sub-crystalline aspect. There is, also, a plumba- 

 ginous appearance in the anthracite found in these rocks, which does 

 not exist, except in the carbon of the older intermedial and primary 

 rocks, and which increases with the age of the rock in which it oc- 

 curs. The Rhode Island coal exhibits more of this character than 

 that of Pennsylvania ; and that from Worcester appears much more 

 like mineral carbon than either ; which gradation corresponds with 

 the opinion I have adopted as to the relative ages of these several 

 coal formations. 



Upon the whole we may be certain, I think, that the formation 

 under consideration in Massachusetts and Rhode Island, is a mem- 

 ber of the series generally called transition. But whether it is pre- 

 cisely identical with any European member of that series, I suppose 

 we do not yet possess the data for determining. The only organic 

 remains yet found in this formation are vegetable ; which will not 

 enable us even to prove that it belongs to the transition series, if a re- 

 mark of Al. Brongniart be true, that "no species of plant has been foun % d 



* Superposition of Rocks, p. 201. 



f Geological Manual, p. 433. 



32 



