These tuffs of the southern shores of the Grand Canary, containing the Upper Miocene shells, appear to be about the same age as the most ancient volcanic rocks of the island, composed of slaty Diabase, phonolite, and trachyte.
"The Student's Elements of Geology"
Sir Charles Lyell
Some investigators of these ores believe them to have been introduced into the conglomerate and sand by later solutions, possibly by hot solutions related to certain Diabase intrusions that cut the beds.
"The Economic Aspect of Geology"
C. K. Leith
The ores are found in numerous short, narrow veins, principally in pre-Cambrian sediments near a thick quartz-Diabase sill.
"The Economic Aspect of Geology"
C. K. Leith