464 



ME. 0. A. DERBY GIST 



is suggestive of denuded hills of leucite rock buried beneath, a flow 

 of phonolite. The former rock occurs in the little valley between the 

 two cuttings, the relative position of which is very much as repre- 

 sented in the figure, so that it is probable that the two masses are 

 connected underneath a capping of phonolite. The peculiar-shaped 

 detached mass in the left-hand figure can hardly be a dyke, and is 



Fig. 3. — Sections on Railway near Pinlialzinlio. 



a. Decomposed leucite rock. 



b. Decomposed phonolite. 



perhaps a fallen boulder enveloped in the phonolite. It is 4 miles 

 wide in the widest part and lies about 20 metres away from the 

 main mass. In the cuttings in leucite rock below Pinhalzinho 

 several dykes, from 2 to 4 metres wide, occur, some of which are 

 evidently of decomposed phonolite, while one, which is better pre- 

 served, although altered to some extent, is either a trachytic rock 

 or a more felspathic phonolite than any elsewhere observed. 



In the bends of the tunnel and of Pinhalzinho there are considerable 

 cuttings in dark blue phonolite and in a peculiar red rock intimately 

 associated with it. The latter is best preserved at the tunnel ; 

 but even there, although the rock is apparently perfectly sound, its 

 brisk effervescence with acid shows that a part of its original con- 

 stituents have been transformed into carbonates. Under the micro- 

 scope, I could make nothing out of it beyond the occurrence of 

 minute dark microlites in a very finely granular ground-mass. In 

 places, dark red glassy crystals of hexagonal outline and irregular 

 whitish spots occur sparingly : both appear to be of secondary 

 origin. Generally the rock appears very homogeneous, but in 

 places thin undulating streaks of lighter and darker red, giving an 

 appearance of fluxion-structure, are seen. In other places there are 

 patches and streaks of bluish and greenish phonolite, which appear 

 to shade off into the red rock without well-defined outlines, such 

 as would be expected if they were foreign inclusions. Patches 

 of included pebbles and boulders with well-defined rounded out- 

 lines are also seen ; and two or three large cuttings near Pinhal- 

 zinho are exclusively through a coarse boulder- conglomerate, which 

 is, however, so much decomposed that only on the closest scrutiny 

 can it be distinguished from the ordinary red rock. This con- 

 glomerate is well exposed in a ridge just above the tunnel, inter- 

 calated between two closely adjacent ridges of the red rock, and 

 passed by a cutting about 80 metres long and 15 metres high, in 

 which hundreds of broken boulders with perfectly fresh fracture are 

 seen. They are all well rounded and of all sizes up to a cubic 



