was that here inferred for those of the Lower Rhine--viz., the close of the Miocene stage--and from evidence subsequently to be adduced from other European districts, it will be found that there was a very widely spread outburst of volcanic action at this epoch. (_c._) _The Range of the Siebengebirge._--This range of hills--formed of the older volcanic rocks of the Lower Rhine--rises along the right bank of this noble river opposite Bonn, where it leaves the narrow gorge which it traverses all the way from Bingen, and opens out on the broad plain of Northern Germany. The range consists of a succession of conical hills sometimes flat-topped--as in the case of Petersberg; and at the Drachenfels, near the centre of the range it presents to the river a bold front of precipitous cliffs of trachyte porphyry. The sketch (Fig. 21) here presented was taken by the author in 1857 from the old extinct volcano of Roderberg, and will convey, perhaps, a better idea of the character of this picturesque range than a description. The Siebengebirge, although appearing as an isolated group of hills, is in reality an offshoot from the range of the Westerwald, which is connected with another volcanic district of Central Germany known as the Vogelsgebirge. The highest point in the range is attained in the Lohrberg, which rises 1355 feet above the sea; the next, the Great Tränkeberg, 1330 feet; and the next, Great Oelberg, 1296 feet. [Illustration: Fig. 21.--The Volcanic Range of the Siebengebirge, seen from the left bank of the Rhine, above Bonn.--(Original.)] The range consists mainly of trachytic rocks--namely, trachyte-conglomerate, and solid trachyte, of which H. von Dechen makes two varieties--that of the Drachenfels, and that of the Wolkenburg. But associated with these highly-silicated varieties of lava--and generally, if not always, of later date--are basaltic rocks which cap the hills of Petersberg, Nonnenstrom, Gr. and Ll. Oelberg, Gr. Weilberg, and Ober Dollendorfer Hardt. The question whether there is a transition from the one variety of volcanic rock into the other, or whether each belongs to a distinct and separate epoch of eruption, does not seem to be very clearly determined. Mr. Leonard Horner states that it would be easy to form a suite of specimens showing a gradation from a white trachyte to a black basalt;[5] but we must recollect that when Mr. Horner wrote, the microscopic examination of rocks by means of thin sections was not known or practised, and an examination by this process might have proved that this apparent transition is unreal. According to H. von Dechen, there are sheets of basalt older than the greater mass of the brown coal formation, and others newer than the trachyte;[6] while dykes of basalt traversing the trachytic lavas are not uncommon.[7]