160 T. 0. Bosicorth — Birth of an Island near Trinidad. 



The Tertiary strata of Trinidad consist of clays and lenticular, 

 current-bedded sandstones, the whole sequence displaying remarkable 

 lateral variation. Along the anticlines, which generally are sharp 

 and very steep, petroleum has accumulated where the conditions are 

 favourable, and its presence is manifested by escaping gas, seepages of 

 oil, and by extensive surface spreads of pitch. In some places occur 

 beds of clay-shale, which have become burnt (probably at depth) into 

 red 'brick' by the spontaneous combustion of the hydrocarbons 

 contained. 



JVeiffhiourin^ Mud Volcanoes. 



Along the Southern Anticline ' mud volcanoes' are a chai'acteristic 

 feature. These are commonly cones of mud with a crater at the top 

 from which issue gas, oil, salt water, and mud. The majority are only 

 a few feet high, but some are much larger. Others again are but 

 slightly conical, and appear as mud springs sometimes several hundred 

 feet across. About forty mud volcanoes and groups of volcanoes are 



South. Wesf Corner 

 of 



TRINIDAD. 



Mud Volcanoes indicated ^ 

 In/ large dots. 



CedrosPt. 



known to the writer on this one anticline, and as a rule they are so 

 truly situated on the crest that where rock exposures fail they have 

 afforded invaluable evidence for mapping the anticline. 



One of the largest of these volcanoes is at Chagonary Point, 

 about 1^ miles east of the new island. Mr. Cunningham Craig says 

 of it : ^ " The circular area of barren mud marking the crater is some 

 80 yards across, and a flow of mud has descended to the beach 

 a distance of 250 yards. Trees one foot in diameter have been broken 

 and the upper part thrown away from the centre of the outburst. 

 Blocks of rocks up to 15 inches in diameter have been brought up 

 from beneath the surface and scattered about the mud crater. They 

 consist of ironstone nodules, nodules and crystalline groups of pyrites, 

 Cretaceous pebbles, coarse Tertiary grit, and fine pale sandstone with 

 plant remains and calcite vein-stuff, A bituminous odour is noticed 

 on all the porous ejected fragments and in fact a smell of petroleum 

 pervades the whole locality." 



Another large one is the Columbia volcano near Cedros, about ten 



^ Council paper No. 119, Trinidad, 1905. 



