RAYMOND: CORRELATION OF THE ORDOVICIAN STRATA. 189 



These layers are often vividly colored, l^eing 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 conies a band, 

 thirteen feet in thickness, of thin-bedded, shaly limestone and shale 

 in which Asaphus broggeri and Onchomctopus volborthi are foulid. 

 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 hpidurus and Megalaspis gibha in numbers. At the top 

 of the formation is another thinner-bedded, softer, gray and green 

 limestone, characterized by a great abundance of Asaphus cxpansus, 

 and containing also A. lamaiiskii, and Xilcus armadillo, this limestone 

 being about ten feet thick. This makes the total thickness of the 

 formatidn 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 Onchomc- 

 topus volborthi fauna, while at the top, Asaphus Icpidurus and Megalas- 

 pis gibba are found. The layers with ^isaphus e.rpansus 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, Onchomctopus volborthi, and Asaphus 

 Icpidurus, persist as far west as Reval, though further west the Asaphus 

 Icpidurus fauna is lost, and of the zone with Asaphus broggeri and 

 Onchomctopus volborthi only a thin remnant remains in the section at 

 Packerort. At this latter locality the green sand has the greatest 

 thickness known, eleven feet, fpllowed by two and a half feet of hard 

 green limestone with large grains of glauconite and many trilobites, 

 among them Mcgcdaspis planilimbata, then one foot three inches of 

 thin-bedded limestone and shale, this containing Asaphus broggeri. 

 The limestone of the formation is therefore only three feet and nine 

 inclies 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 



