■60 T. Barron — Age of the Petrified Forest, etc., 



Tellowstone Park were not necessary to the formation of Gebel 

 Ahmar Sandstone ; hot springs were capable of doing all that is 

 required. He imagines dunes and marshes, fresh-water basins or 

 lagoons containing silica, and sand which was borne by fluviatile 

 or a3olian agencies and disposed in an irregular manner in the 

 neighbourhood of the springs. This was cemented together by the 

 silica contained in the water. This author regards the Gebel Ahmar 

 Sandstone as Oligocene, while the silicified forests he makes Lower 

 Miocene in many places. 



It is now necessary to give the views of the present writer 

 regarding the age of the beds in question. In the neighbourhood 

 of Cairo there exists an area covered with petrified trunks of trees 

 which is known as the Petrified Forest. These tree-trunks, now 

 lying on the surface, have been exposed by the removal of the 

 sands, etc., in which they were originally embedded. There is no 

 evidence for the idea that these trees were silicified in situ ; there 

 is little doubt that they have been carried thither by a river and 

 deposited in an estuary or lagoon. 



The beds in question, if traced northwards, can be seen to 

 disappear under the thin sheet of basalt underlying the Lower 

 Miocene beds. This is the case in every place in this district where 

 these two formations are seen in contact. 



As a proof that the silicification of the tree-trunks did not take 

 place at the time they were deposited, one may point to the entire 

 absence of bark in every instance, the complete lack of remains of 

 leaves and branches, and in many instances the marks of decom- 

 position in the trunks which must have taken place prior to 

 silicification. Another proof is the fact that the thermal springs 

 were subsequent to the outpouring of the basalt. Evidence of this 

 is seen in Gebel Gafeisad or Agleiat Qamr (a volcanic neck), where 

 the hard plug of silica filling up the throat of an old thermal spring 

 stands right in the centre of what was the neck of the volcano. 

 From this radiate hard veins of silicious rock which are the in- 

 filling of fissures out of which welled the warm ^ilicated waters 

 which did the work of petrification. 



North of Der el Beda, the ruined palace of one of the Pashas, 

 there occurs another volcanic neck, with a large dyke-like mass 

 of quartzite running through it, which is undoubtedly the result of 

 the plugging up by sand and colloid silica of a fissure up which 

 the silicated waters rose. Round these two places numerous 

 examples of plugged fissures are seen, while a certain area of the 

 sand around has also been consolidated. 



To the north-east of Bir Gendali and about 10 kilometres down 

 Wadi Gendali there occurs what appears to be an injected fissure 

 out of which basalt issued at one time. Connected with this, and 

 standing out in relief, is the plug of a geyser or very large thermal 

 spring opening. Here the relations between the basalt and the 

 silicious rock are the same as those observed at the other places 

 above mentioned, that is to say, the basalt was prior to the formation 

 of the silicious plugs. It is interesting also to notice that in the 



