RAYMOND: CORRELATION OF THE ORDOVICIAN STRATA. 185 
Kunda, Ontika, Peuthof, and Papowka, and studied especially the 
contact of the Cambrian and Ordovician near Baltishport and at 
Narwa. The best section seen was at the cliff Peuthof, which is 
north of the station Waiwara, a few miles west of Narwa. Alternating 
strata of light colored sandstone and blue clay-shale were there well 
exposed, but the strata can be studied more in detail at Port Kunda, 
where Mickwitz found specimens of Schmidtiellus mickwitzi, the 
mesonacid which first afforded definite pupa of the Lower Cambrian 
age of these strata. 
It has been repeatedly stated that the “Blue Clay” underlies the 
sandstone of the Cambrian, but I did not find this to be the case. 
Everywhere the highest layer of the Cambrian appeared to be a hard, 
usually almost white, sandstone. The upper bed, where its thickness 
could be seen, was usually not over fifteen to twenty-five feet thick, 
and beneath it was a bed of blue clay-shale of variable thickness. 
Below this again one finds sandstone and alternations of shale and 
sandstone continue to the base of the cliff, and, according to borings 
in Reval and Petrograd, such alternations continue downward about 
600 feet to the gneiss. The fossils have been found in the upper zones, 
within fifty feet of the top of the formation, and there is no reason to 
believe that strata of any age other than Lower Cambrian are present 
in this formation. The “Blue Clay” of the Lower Cambrian has 
received considerable notoriety, as it has often been reported as a soft, 
unconsolidated blue clay which could not be distinguished from clay 
of glacial age. Masses of this sort were seen at two places, at Papowka 
south of Petrograd, and on the shore at Ontika. In neither case was 
the clay actually in position either under or between layers of sand- 
stone, but it lay in such a position that it could be readily conceived 
that it was Cambrian clay which had worked out from a layer nearby. 
In both cases it was very full of water, and it is probable that it 
represented a portion of a stratum of shale which had been worked 
up by the action of frost, water, and a creeping movement, until all 
traces of the original stratification had been destroyed. Where mined 
from the layers for the cement plant at Port Kunda, the clay is well 
stratified, and hard. It is, however, very fine grained, soapy to the 
touch, and a very fine plastic clay. The quickness with which it loses 
its stratification on weathering is probably due to its fine grain and 
the readiness with which it takes up water, rather than to the fact 
that it has never been consolidated. 
In discussing the finds of “Olenellus” at Kunda and near Reval by 
Mickwitz, Marcou (31) proposed for the Lower Cambrian strata as 
