1855.] MURCHISON AND MORRIS — THURINGERWALD. 423 



Dresden, we were much struck with a natural section which exhibits 

 the intimate dependence of this coarse conglomerate upon contiguous 

 eruptions of porphyry. On quitting the plateau of the so-called 

 "gneiss" of Freiberg (a crystalline stratified rock, which we have 

 elsewhere speculated upon as being probably nothing more than 

 metamorphic Silurian *, and which is penetrated here and there by 

 granite), we passed over a great breadth of red porphyry, on the 

 western boundary of which, and in the deep gorge of Thar^dt, the 

 igneous rock is exposed in towering pinnacles, and is clearly seen to 

 have penetrated the gneiss, which extends eastwards to near the vil- 

 lage of Hainsberg. On approaching the latter place, powerful con- 

 glomerates of the Rothe-todte-liegende are seen resting in inclined 

 positions on the eastern flank of the gneiss and crystalline rocks. 

 These conglomerates, which are considered by Geinitz to lie in the 

 upper part of the formation, are made up essentially of the gneiss 

 and granite of the adjacent hills through which the porphyry has 

 risen up, and have therefore directly resulted from that intrusive 

 igneous agency. The blocks are often of several feet diameter, and on 

 the whole the mass reminded us much of the coarse conglomerate of 

 the Old red sandstone on the north flank of the Ord of Caithness. 



In the deep ravines E. of Dresden, leading into the Plauensche- 

 grund, into which, in company with Prof. Geinitz, we descended 

 from plateaus of overlying horizontal sandstones of the Cretaceous 

 group, we examined other rocks of the Rothe-todte-liegende which 

 there overlie the coal, and saw the following descending order : — 

 1. Conglomerate. 2. Variegated deep red shale with green spots. 

 3. Pink-coloured porphyry, which, though a true igneous rock, is 

 as regularly stratified and jointed as the red strata with which it 

 alternates. It is the " Schlam-lava" of Geinitz, and offers in truth 

 the most perfect evidence of having been a coulee formed during 

 the agglomeration of the Rothe-todte. Thus far the section is open 

 to view on the side of the hills ; the remainder is known through 

 the sinkings for the underlying coal. According to the working 

 plan of a very intelligent manager of the works at Hainichen, the 

 shafts passed down through about 500 feet of other massive alter- 

 nations of the Rothe-todte, alternating with porphyries, before the 

 first traces of coal were reached. The best bed of coal has a 

 thickness of about 3 feet, and was first worked at a depth of 

 158 lachter or about 1100 English feet. It was soon lost in this 

 its first and horizontal position, and was subsequently regained in 

 a highly inclined position on the slope of the hill, 48 lachter beneath 

 the upper level. When we visited the spot another sinking was being 

 made somewhat lower on the hill side, through 800 feet of the Rothe- 

 todte, to win the coal in a deeper part of the valley. The works in 

 the Plauensche-grund leave therefore no room to doubt, that whilst 

 the coal strata were here originally quietly deposited on gneiss and 

 other ancient rocks, they were subsequently penetrated by eruptions 

 of porphyry accompanied by great dislocations, which broke up the 

 carboniferous rocks and left them at the very different levels and at 



* ' Siluria,' p. 361. 



