Clay is described as; "a finely-grained natural rock or soil material that combines one or more clay minerals with possible traces of quartz, metal oxides and organic matter."
Shales is also; " a fine-grained, clastic sedimentary rock composed of mud that is a mix of flakes of clay minerals and tiny fragments (silt-sized particles) of other minerals, especially quartz and calcite."
Both of these are fine-grained and consist of rock & soil and quartz.
The most consistent way to obtain information about the evolution of species is to look at the fossil record. Another is to observe the differences between species currently on earth. Another is to use carbon dating.
