302 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



The eastern limit of the basalt is pretty correctly marked across 

 the Plain of Selmas by numerous little rounded knolls of this rock, 

 which extend along a line drawn from the east of Kalah Kami, on 

 the south, to the Derik stream on the north. 



Soon after quitting the village of Selmas, on the road to Derik, the 

 red sandstones which were previously observed on the descent from 

 the Anjulukh Pass, again appear from beneath the rich alluvial soil 

 of the plain. The beds dip on their first appearance at an angle of 

 20° to the south, but this dip increases in ascending the ravine of 

 the Derik stream, until the beds become perfectly vertical. Layers 

 of gravel-conglomerate are associated with the upper part of the 

 sandstone-series. In one locality a thin bed of loose gravel rests 

 on the broken edges of the sandstones, and is overlaid by an hori- 

 zontal deposit of cream-coloured travertin. The vertical sandstones 

 and the travertin are again covered by the basalt, which dips at an 

 angle of 2° to the south. Towards the north the basalt gradually 

 decreases in thickness, becoming less columnar and more vesicular, 

 until it finally dies out somewhat abruptly on the west bank of the 

 ravine, where it overlies a considerable bed of travertin. On the 

 east of the stream, the basalt only occurs in one insignificant patch, 

 upon the summit of a small peak of sandstone. Wherever the tra- 

 vertin is in contact with the basalt it is rendered hard and compact. 



In the bed of the stream are blocks of pink basaltic scoriae, similar 

 to those which were observed in connexion with the basalt in the 

 Chehrik Cliffs, near Kalah Kami ; but they contain a much larger 

 quantity of calcareous matter. Further up the ravine the tufa 

 exhibits much contortion, and is penetrated by a peak of dark- 

 coloured heavy rock of decomposing felspar mixed with dark car- 

 bonate of lime. Upon the sides of this peak are several detached pieces 

 of tufa, torn away from the parent mass, and so metamorphosed, 

 that it would be almost impossible to recognize it in the pure white 

 marble into which it has been converted, were it not that we can 

 trace it through all its phases. In some instances it bears a remark- 

 able similarity to some of the beds of Nummulitic limestone in the 

 south. Passing onwards to the north of the felspathic peak, we 

 again have the tufa contorted, and resting against and upon it. It 

 afterwards bends down towards the little village of Derik, where 

 powerful springs are now in action, producing travertin in abundance, 

 and showing the agency which deposited the older and altered tufa. 

 The narrow valley of Derik is bounded on the north by high moun- 

 tains of igneous rocks, among which the felspathic and hornblende 

 compounds, so common in this region, are found. 



Travertin Springs. — As calcareous-tufa-springs, from this point 

 northwards, are of continual occurrence, and as the deposits formed 

 by them have vast geological importance, a description of those at 

 Derik, which is a good example of all, is worth recording. 



The springs are close to the village. They are numerous, though 

 two only have any great flow of water. These are about six yards 

 from each other, and rise from the bottom of irregular-shaped 

 basins, between 4 and 5 feet in depth. The water rises with great 



