older Deposits of the North of Germany and Belgium. 249 



out at so many points in these parts of Nassau ; for we quite agree with 

 M. StifFt, that the springs are the still remaining evidences of former plutonic 

 action. 



Schaalstein. — This rock is so dominant and persistent on both banks of the 

 Lahn, the limestone being often completely subordinate to it, that M. StifFt* has 

 fixed upon it as the geological horizon by which the grauwacke and slaty rocks of 

 the Rhine are separated into overlying and underlying deposits. Though this may 

 be a correct observation when applied to parts of the duchy of Nassau, such a 

 mode of distinguishing the age of strata by their mineral condition is seldom tena- 

 ble through large areas. Admitting, therefore, that the peculiar rock called 

 "schaalstein" (whether as seen on the Lahn, near Dillenburg, or near Brilon) 

 is for the most part associated with strata of an age intermediate between the car- 

 boniferous and Silurian epochs, we cannot invariably so define its position ; for 

 some portions of it are found to alternate with beds of the underlying system, 

 especially the grauwacke which ranges up to the north flank of the Taunus. (See 

 PI. XXIII. 'fig. 9.) 



But what is this schaalstein ? We answer, that this protean rock has clearly originated in submarine 

 plutonic action. Notwithstanding this origin, it is a completely bedded rock which alternates with lime- 

 stone and shale, and occasionally contains organic remains ; is regularly jointed ; and assumes, in short, 

 every character common to deposits which have been formed by submarine action. After describing 

 all the varieties in the composition of schaalstein, M. StifFt places it as a rock intermediate between schist 

 and greenstone. The schistose varieties alternate with the underlying strata of quartzose grauwacke 

 and contain much lime and talc (chlorite ?). The greenstone varieties consist of various forms of stra- 

 tified trap, sometimes fine amygdaloidal, sometimes in the form of a trap breccia, and gradually pass 

 into flaggy and porphyritic greenstone. The prevalent varieties, however, are made up of thin broken 

 plates of schist and chlorite, mixed up with decomposing felspar, some sand, and much carbonate of lime ; 

 the whole so arranged as to flake or shale off under the hammer, and hence its name (schaalstein or shale 

 stone f). In many situations it is copiously charged with chlorite, in others with iron ore, but white 

 calcareous spar is perhaps the most common subordinate ingredient ;{:. 



Though finely laminated and occasionally very shall/, it is often thick-bedded, and is then (particularly 

 if the lime and other ingredients be equably diffused) a very good building-stone ; and it is much quarried 

 for that purpose, as it is easily worked. Its colours are of course as various as its composition ; viz. 

 greenish, greyish and reddish. In one word, it is a plutonic recomposed rock ; the description of any 

 portion o( which, taken from that end of the series where it is in contact with greenstone and porphyry, 



* Geognostische Beschreibung der Herzogthums Nassau, 1831, p. 4-63 et seq. ; see also Leonhardt's 

 Char der Felsarten, 1823, p. 747. 



t According to Von Dechen, to whose beautiful inedited map of this region we have already alluded, 

 the " schaalstein " (an equivalent or variety of the Variolite of the French) is a metamorphic rock con- 

 nected with Labrador porphyry. 



X Sir A. Crichton has described this rock, Geol. Trans., 2nd Series, vol. ii. p. 269, to which we further 

 wish to refer the reader. 



