A few explanatory remarks concerning the mode of detection of Precambrian rocks may not be amiss.
We may take our own country as a region where a good development of the Precambrian rocks occurs.
These Torridonian strata furnish us with the most satisfactory group of Precambrian sediments yet detected in Britain.
The period of geologic time between Hadean Time and the Phanerozoic Eon, from about 3.8 billion to 540 million years ago. During the Precambrian Eon, which is divided into the Archean and Proterozoic, primitive forms of life first appeared on Earth. See Chart at geologic time.