468 PROCEEDINGS OP THE GEOLOGICAL SOCIETY. [May 16, 



from the assumption of a plastic condition, to which property its 

 frequent delivery at the surface is partly referable ; where the 

 latter is hollow or basin-shaped, the bitumen accumulates, forming 

 deposits such as the well-known Pitch -lake. Sometimes the emis- 

 sion is in the form of a dense oily liquid, from which the volatile 

 elements gradually evaporate, leaving a solid residue. 



Mineral pitch is also extensively diffused in the province of Ma- 

 tuxin, on the main (the other districts of the Llanos were not suffi- 

 ciently examined to determine its existence, which, however, is 

 generally affirmed), and in still larger quantities near the Gulf of 

 Maracaybo, on the northern shores of New Granada, and in the 

 valley of the Magdalena, where it probably is a product of the 

 same tertiary formation. 



The phenomenon of salses or mud-volcanos, consisting of the 

 solution of inflammable gas accompanied by the discharge of a 

 muddy fluid and asphaltic oil, is perhaps closely related to the 

 activity just described, as carburetted hydrogen may be disengaged 

 in the direct formation of asphalt*. Several of them occur in Tri- 

 nidad also, in the " Newer Parian." They were likewise observed in 

 the province of Maturin, presenting similar characters. At Turbaco, 

 near Carthagena, precisely the same action is manifested, but on a 

 much larger scale. This is further confirmatory of a great extension 

 of the above formation to the westward. 



The thermal waters of Trincheras, near Yalencia, issuing from 

 mica-schist, contain merely traces of silica, sulphuretted hydrogen, 

 and nitrogen, and possess a variable temperature, as shown by the 

 following determinations : — 



Humboldt, in 1800 194° 



Boussingault, in 1823 206° 



The author, in 1859 198° 



The hot springs of Chaquaranal, near Pilar, in a limestone of the 

 " Older Parian," are of a highly interesting nature, presenting the rare 

 phenomenon of waters discharged at, and even over, the boiling- 

 point. There are several centres of issue, situated in adjacent 

 ravines. Sometimes the fluid is delivered under pressure, rising in 

 a jet, continuing in a state of ebullition for several feet from the 

 point of discharge, accompanied by a forcible evolution of steam, 

 and depositing abundance of calcareous matter. The fissures of the 

 adjacent rock are lined with spathose crystallizations, and the 

 acicular forms of sulphur. The vapours escaping from these fissures 

 consist principally of steam. 



A species of Souffriere, termed the " Azufral grande," only half a 

 mile distant, comprises several orifices, from which heated vapours, 

 strongly impregnated with sulphuretted hydrogen, are evolved ; the 

 sides of the cavities are coated with quantities of large crystals of 

 sulphur ; and the adjacent surface, for an extent of a quarter of an 

 acre, is covered by a variety of purely siliceous deposits, sometimes 



* A detailed description of the salses of Trinidad is contained in Appendix 

 H. of the ' Report.' 



