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RAYMOND: CORRELATION OF THE ORDOVICIAN STRATA. 189 
These layers are often vividly colored, being generally red or purple 
with patches and spots of green and yellow, and usually contain 
quantities of rather large green grains of glauconite. The characteristic 
fossil is Megalaspis planilimbata. Above these layers comes a band, 
thirteen feet in thickness, of thin-bedded, shaly limestone and shale 
in which Asaphus bréggert and Onchometopus volborthi are found. 
These strata weather to a soft gray mass, and above them are harder 
layers of limestone with less shale, making the fourth division, eleven 
feet in thickness. This also is a blue-gray limestone, and contains 
Asaphus lepidurus and Megalasyis gibba in numbers. At the top 
of the formation is another thinner-bedded, softer, gray and green 
limestone, characterized by a great abundance of Asaphus expansus, 
and containing also A. lamanskii, and Nileus armadillo, this limestone 
being about ten feet thick. This makes the total thickness of the 
formation on the Walchow and Lawa about forty-six feet. 
When followed westward this formation becomes thinner and 
usually at the expense of the upper members, though the green sand 
may thin to practical disappearance. Thus, on the Papowka, the 
green sand is only one foot thick, the Megalaspis planilimbata or 
lowest limestone bed is seven feet thick, and is followed by twelve feet 
of shaly limestone, the greater portion of which contains the Onchome- 
topus volbortbi fauna, while at the top, Asaphus lepidurus and Megalas- 
pis gibba are found. The layers with Asaphus expansus are gone 
entirely. Further west, the shale almost entirely disappears from this 
part of the section, though there is usually a thin shaly layer or a 
shaly parting. The limestone of the section becomes very thin, but 
the three faunas, M. planilimbata, Onchometopus volborthi, and Asaphus 
lepidurus, persist as far west as Reval, though further west the Asaphus 
lepidurus fauna is lost, and of the zone with Asaphus bréggeri and 
Onchometopus volbortht only a thin remnant remains in the section at 
Packerort. At this latter locality the green sand has the greatest 
thickness known, eleven feet, followed by two and a half feet of hard 
green limestone with large grains of glauconite and many trilobites, 
among them Megalaspis planilimbata, then one foot three inches of 
thin-bedded limestone and shale, this containing Asaphus bréggeri. 
The limestone of the formation is therefore only three feet and nine 
inches in thickness, the two younger faunas are absent entirely, and 
the strata containing the others are very thin. Besides the absence of 
the younger faunas there is other evidence which indicates that erosion 
has taken place since the deposition of the upper strata of this forma- 
tion. In the section at Packerort, the thin-bedded limestone is fol- 
lowed by a conglomerate in which there are large numbers of pebbles 
