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These strata are less connected by alternation than by opposition. Porphyritic breccias which envelope the quartzose porphyries. The gem-salt oscillates from zechstein to muschelkalk. Tertiary strata, showing a much smaller number of dicotyledonous plants. These alternations and transitions appeared to me less common in the littoral Cordillera of Venezuela than in the Sierra Parime.
How can we in many circumstances determine the analogy existing between a limestone with but few petrifactions and an intermediary limestone and zechstein, or between a sandstone superposed on a primitive rock and a variegated sandstone and quadersandstein, or finally, between muriatiferous clay and the red marl of England, or the gem-salt of the tertiary strata of Italy?
Gold, platinum, silver, mercury, copper, gem-salt, sulphur and alum may become objects of important workings.
The co-ordinate layers of gem-salt, muriatiferous clay and gypsum present the same difficulties in both hemispheres; these masses, the forms of which are very irregular, everywhere exhibit traces of great commotions. Sometimes gem-salt appears to oscillate between variegated sandstone and muschelkalk. I made two excursions on the peninsula of Araya.
Now, in the peninsula of Araya, and in the island of Marguerita, saliferous clay impregnated with bitumen is met with in connexion with this early formation, nearly as gem-salt appears in Calabria in flakes, in basins inclosed in strata of granite and gneiss.
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