That’s exactly what he said:
There is only one layer that could possibly be described as “lower shale layer”, and it’s the correct one. He even quoted the page as saying:
Above the non-conformity (represented in red) is a Lower Cambrian sequence.
The Lower Cambrian sequence misses at this location the Zabriskie Formation (which is found immediately to the right of the area) and starts with the trilobite-rich Latham Shales, followed by the oncolite-rich Chambless Formation.