Correlation of Lower Cambrian rocks is hampered because there are no widespread and rapidly evolving organisms such as the later agnostids, graptolites, conodonts, ammonites, or planktonic foramini fers, that might provide basis for a consistent intercontinental biostratigraphy. Four problems illustrate issue: 1) age oldest trilobites China; 2) acritarch correlations between Siberia Baltica; 3)...

In the last few years the problem of the lower boundary of the Cambrian has been dealt with in dozens of works which considered not only the history of the question but all the current material available. It is a subject discussed at many national and international symposia. Although great progress has been achieved in drawing together the points of view on the position of the boundary (compare...