MIDDLE AND UPPER ORDOVICIAN. 



217 



Ulrich (personal communication) comments as follows on the section: 



These Ordovician fossils are in the conglomerate bowlders here as at Point Levis. The 

 graptolitic shale itself is the Levis thrust inland over the Chazy. The remainder of the section 

 is in question. It may be in part Chazy or all post-Chazy, with persisting Chazy species, as in 

 the Liberty Hall limestone of Virginia. 



M-N 14. LAKE WINNIPEG DISTRICT, MANITOBA. 



Dowling^*" gives the following table of divisions of the later Ordovician in the 

 Lake Winnipeg region and compares them with the formations known in Minnesota. 



« This is the widely spreading zone so well displayed at Silliman Mountain, Baffin Land. The Winnipeg sandstone 

 of Manitoba is probably at the same horizon but may be in part St. Peter. — Comment by E. 0. Ulrich on manuscript. 



Dowling describes the several divisions of the Ordovician as follows: 

 The basal beds of the Cambro-Silurian [Ordovician] of Manitoba consist of a series of soft 

 friable sandstones, shaly in the upper part but generally similar to those found in Minnesota 

 beneath the Trenton limestone. Very few fossils have been obtained, and those from the upper 

 part only, denoting merely' lower beds of the Trenton. * * * The fossils give no definite 

 information as to the age of the beds but suggest a passage from Black River to Trenton. * * * 

 In eastern Canada and New York State the Black River is usually a thick-bedded limestone, 

 but in. Minnesota it is composed mainly of greenish shales, so that the shales below the limestone 

 in the borings at Rosenfeld and Selkirk may be taken as the passage beds from the Black River. 

 These are represented on Lake Winnipeg by shaly bands in the upper part of the section. The 

 sandstone below, being in the nature of a shore deposit, though occupying a position nearly 



