The Pre-Cambrian Era

Abstract

The Pre-Cambrian covers a vast stretch of time during which the main character of the rocks from the present point of view is that fossils cannot be used to correlate them. A few interesting fossils have been found in the younger Pre-Cambrian rocks, but it remains generally true to say that there are none of stratigraphical value. Isotopic dating is therefore of great value and most correlation of Pre-Cambrian rocks is based upon it, especially as the majority of these old rocks have been metamorphosed and thus contain abundant minerals suitable for isotopic analysis, such as biotite mica, or are cut by numerous igneous intrusions and mineral veins containing such minerals.