3TB. 0. A. DERBY OX 



chert, this last being a very characteristic feature of the Carboniferous 

 series of Sao Paulo. 2s~o fossils could be found, and its complete 

 identity with the Carboniferous series could not be satisfactorily 

 established, since it is possible, though not very probable, that two 

 distinct formations in this region may be characterized by cherry 

 layers. If it is distinct I am very strongly of opinion that it 

 will prove to be older rather than newer. The beds are inclined at 

 an angle ot 15° to the eastward i^away from the mountain), strike 

 X. :20 c W. So high an inclination is unusual in the series to which 

 this rock is referred, which, whenever it has been examined, is essen- 

 tially horizontal or with only slight local inclination. As. however, 

 the eruptive activity of this region continued after the sandstone 

 was deposited, the disturbance may be regarded as local. Passing 

 the gap the road bends round and follows the base of the ridge, 

 cuttings in sandstone appearing for a distance of two or three kilo- 

 metres. In some of these the rock is seen to pass into a tuffaceous 

 conglomerate containing pebbles of quartzite, and pebbles and 

 boulders of eruptive rocks. A peculiar feature of this conglomerate- 

 is the presence of abundant and often large masses of brown mica, 

 which, from its occurrence in masses of considerable thickness and of 

 almost perfect crystalline form, not in detached ilakes. must have 

 been formed in place after the coarser material of the rock was 

 deposited. 



In the cuttings both the sandstone and the conglomerate are con- 

 siderably decomposed, and the contact is not perfectly clear. In one, 

 sandstone is seen above, conglomerate below, with no apparent line 

 of demarcation between them, although the passage from coarse con- 

 glomerate to fine-grained and homogeneous sandstone is an abrupt 

 one. That an actual passage occurs seems to be confirmed by the 

 fact that in the coarser parts of the conglomerate, and near the 

 supposed contact, the cement is extremely quartzose. whereas further 

 away and in the finer portions the eruptive elements predominate 

 in the cement, and the same rock with its characteristic crystals of 

 mica presents the aspect of an ordinary tuff. The predominant 

 types among the boulders of the conglomerate are two rocks which 

 were not found satisfactorily exposed in situ. One has the external 

 aspect of a moderately coarse-grained diabase, which, under the 

 microscope, shows remarkably fresh plagioclase as a predominant 

 element, the other elements being altered beyond recognition by me, 

 and in a manner which I have never seen in any diabase. From 

 its behaviour with acids it appears to contain nepheline, in which 

 case it is probably a teschenite. The other rock common in the 

 boulders seems to me to be a somewhat altered phonolite. but. if so, 

 it is much richer in iron than any undoubted phonolite that I have 

 examimed. Undoubted specimens of phonolite also appear in the 

 conglomerate. 



In one of the cuttings in sandstone a dyke of phonolite occurs, 

 also a dyke of a rock too much decomposed for positive recognition, 

 but which appears to be identical with the diabase-like rock of the 

 boulders. In another cutting in conglomerate there is an inclined 



