CAMBRIAN AND LOWEE ORDOVICIAN. 139 



ripple-marked layers replete with worm burrows, worm trails, and other marks of a shallow- 

 water origin. * * * 



In the outer areas of the Cambrian rocks of the Atlantic coast the Etcheminian terrane is 

 easily traced by the prevailing red color, as well as by its fossils. In this outer zone fine slates 

 prevail and there are beds of limestone, as may be seen in the Massachusetts and Newfoundland 

 areas. In the inner zone (New Brunswick and Cape Breton) the sediments are coarser and 

 limestones are wanting; it is in this inner zone that a middle member of sandstones and flags is 

 most distinctly marked. 



The organic remains of this middle member are similar to those of the lower sediments, so 

 that the Etcheminian -rocks have only two faunas, an upper and a lower. The volcanic rocks 

 beneath them have yielded a scanty fauna, which may not be more than a subfauna of the 

 Lower Etcheminian. More material is required to determine the importance of this fauna. 



So far as the St. John terrane is concerned, it is clear that the basins we have now are but 

 fragments of deposits that have been spread over large areas of the Atlantic coast, and there 

 may be extensive tracts occupied by slates and flags so far metamorphosed that Cambrian 

 fossils can not be recognized. The materials which make up the flags and slates of the Johannian 

 division glisten with water-borne particles of mica, the sands are of uniform texture, and there 

 are no traces of shore lines, though shallow-water beds abound. 



Also the Bretonian division, with its fine-grained dark-gray mud beds holding graptolites 

 and the perfect preservation of its delicate organisms, indicates the presence of a water cushion 

 of considerable depth above its muds, when these were being deposited, a cushion which we 

 can hardly think less than 1,000 feet deep. But a sea of this depth would have covered a wide 

 area along the Atlantic coast, and we therefore infer that the known basins of Cambrian rock 

 are but small fragments of the widespread mantle of sediments that covered this region at the 

 beginning of Ordovician time. 



The group of organic remains of the outer zone of the Etcheminian rocks appears to differ 

 widely from that of the inner. This may be because they do not come from the same time 

 horizon; but it seems more likely to be due to some physical cause, either difference in the 

 depth of the sea in the two zones, or paucity or abundance of sediment in the waters, or difference 

 of temperature of the sea water in the two zones. Whatever the cause, oleneUoid trilobites have 

 not been recognized in the strata of the inner zone, while they are characteristic of the faunas 

 of the outer zone. 



The Etcheminian, St. John, and Bretonian terranes are divided by Matthew 

 into "assises" or faunal zones, and the faunas comprising 380 species are listed 

 accordingly in the paper cited above. 



In earlier papers relating to the Cambrian and pre-Cambrian, Matthew had 

 included the Etcheminian in the latter, as a formation underlying the "Lower 

 Cambrian" (Olenellus zone) . 



Walcott*^^'' studied the sections both in New Brunswick and Newfoundland 

 and reached c6nclusions differing from those of Matthew, which the latter subse- 

 quently accepted, namely: 



(a) The "Etcheminian" terrane of Matthew is of Lower Cambrian age. 



(b) The OleneUus fauna is older than the Paradoxides and Protolenus faunas of the Middle 

 Cambrian. 



(c) The Cambrian section of the Atlantic province of North America includes the Lower, 

 Middle, and Upper Cambrian divisions as defiiied by me in 1891. 



Walcott's conclusions are based on the following sections in part, and others 

 to be found in his paper: ^^* 



Smith Sound section. — On the northern shore of Smith Sound, east and west of Smith 

 Point, the Cambrian rocks are well exposed along the shore. At Broad Cove, west of the point, 



