138 INDEX TO THE STRATIGRAPHY OF NORTH AMERICA. 



Laurentian. — In the column of geological systems, beginning with the oldest or Laurentian, 

 Dr. Matthew has assigned certain crystalline schists of Indiantown and Fairville to this hori- 

 zon. These form a part of the Portland group (lower) of the reports bearing upon the geology, 

 whereas the upper part of this group he classifies as Grenvillian, consisting of clay slates, 

 norites, Hmestones, quartzites, underlain by mica schists. 



Huronian. — The Laurentian Archean rocks are succeeded upwards, as Dr. Matthew points 

 out, by rocks of doubtful Huronian age, consisting of ash-rocks, felsites, diabase, diorite, such 

 as are met with at Carleton Heights and Loch Lomond HiUs, all grouped under the designation 

 "Coldbrook group." Both above and below this Coldbrook group, as well as between the 

 Laurentian of Indiantown and the Grenvillian limestones, slates, etc., of Green Head, Douglas 

 Avenue, etc., a marked discordance of stratification occurs, which apparently indicates long 

 lapses or intervals of time between them. 



Cambrian. — Above the Coldbrook group, and beneath the Cambrian or St. John group, 

 Dr. Matthew describes and classifies certain purplish and green shales, purplish-red sandstones, 

 and coarse red conglomerates, which are exposed on Caton's Island, in King's County, and at 

 Loch Lomond, St. John County, under the term "Etcheminian." 



Between this Etcheminian and the St. John group the discordance of stratification is not 

 as obvious as in the case of the precediag system with the Etcheminian. The fauna of the 

 Etcheminian, however, is essentially a Cambrian fauna according to the writer. 



The Acadian, Johannian, and Bretonian constitute the three divisions which Dr. Matthew 

 has estabhshed in the St. John group. The strata which they represent are 1,650 feet in thickness 

 and consist of mudstones, with slaty cleavage, also sandstones and flags with conglomerate. 

 The uppermost or Bretonian division of the St. John group, which is to be seen in the black 

 graptohtic shales and sandstones of Navy Island and at the falls on the St. John River, near the 

 suspension bridge, are by him referred to the Lower Ordovician. Many of the species which 

 occur here are eminently characteristic of the Levis division of the Qu'ebec group, in the St. 

 Lawrence Valley. These strata correspond to the Skiddaw and Arenig formations of England 

 and Wales and to similar horizons in Scandinavia, France, and elsewhere. 



It is from the Cambrian or lower and most important portion of the St. John group of rocks 

 that Dr. Matthew has obtained material from which he described and illustrated the very 

 extensive extinct fauna and flora of these old Paleozoic sediments. 



In 1904 Matthew ^^^ described the Cambrian as follows: 



Confining our attention to the areas where Cambrian fossfls have actually been found, we 

 note throughout this North Atlantic region the prevalence of volcanic deposits, or of red and 

 green mud beds, in the initial period of Cambrian time. If the former are not actual lava 

 flows, or the cores of old volcanic cones and ridges, they are the compacted ashes, mud, and 

 stones from such a source. 



Resting on these volcanic deposits, though sometimes intercalated with them, are beds of 

 sand and mud that easily show their relation to such a source as the volcano, by the fact that 

 this sand consists largely of feldspathic particles, while the mud beds are pale-green or red 

 accumulations of volcanic dust that have faUen into or been swept into the sea. Hence it would 

 appear that while the first volcanic eruptions occurred over land surfaces, the land soon sank, 

 and the later ones were thrown into the sea. It is in the levigated material thus thrown into 

 the sea, or swept into it by rivers, that we meet with the earliest organic remains of the Cambrian 

 time. These levigated deposits are chiefly in the Etcheminian terrane and contain a very 

 ancient group of Cambrian organisms. They also exhibit a cycle of deposits corresponding to 

 that of the St. John terrane above them, for they have in the middle coarse sandy sediments, 

 that separate two groups consisting largely of mud beds ; of these the lower has conglomerates 

 and sandstones intercalated, while the upper are found to contain flaggy sandstones. 



The principal sandstones, however, are in the middle member, which is comparatively 

 barren of fossils but contains much diffused hematite, giving the rock a markedly red color. 

 These beds also, like those of the corresponding stage of the St. John terrane, frequently show 



