Oct. 4, 1888] 



NA TURE 



55* 



greatest importance for the proper judgment of thti genesis of 

 rocks, do not correspond in the least to the facts, and by a little 

 attention might easily have been avoided. The author has 

 already had occasion to disprove the non-occurrence of frag- 

 ments of clay-slate in the phyllite-gneiss of Goldkronach in the 

 Fichtelgebirge, as maintained by Giimbel. A few hours' search 

 sufficed to collect the clearest examples of abruptly fractured 

 and injected enclosures From this occurrence Giimbel drew 

 widely generalized conclusions. Whether it is enclosed frag- 

 ments or concretions that are contained by a rock, is assuredly of 

 the greatest importance for its proper explication. 



The author then refers to the Ober-Mittweida conglomerate. 

 Roth has described the pebble-like fragments enclosed in this 

 rock, as concretions. The author cannot agree with him in this 

 determination, and gives his reasons, which are mainly based on 

 petrographical considerations, why he does not do so. 



It will hardly be denied that dynamic processes involved in 

 mountain-building, be the latter referred to whatever cause one 

 wdl, have not only not been without influence on the structure 

 of the ricks already in existence, but have also considerably 

 influenced the distribution and the intrusion of the eruptive 

 mas es. The observations which the author has published 

 on the gabbros of the Saxon granulite district, on banded 

 granulites, on the conglomerates of the Saxon Erzgebirge that 

 have been metamorphosed to mica-schists, and on Bavarian 

 " Pfahlschiefer," have not been refuted, although their re- 

 examination would not have been attended by any especial 

 difficulties. 



The author then concludes by expressing the wish, that, in the 

 further study of the crystalline schists, metamorphosed sedi- 

 ments, which can, it is true, be altered to true mica-schists, but 

 never to true gneisses of uniform structure, should be kept dis- 

 tinct from those mica-schists of which we do not know the 

 origin, and from the true granitic gneisses. If this be not done, 

 the false conclusion is inevitable that sediments pass through 

 mica-schists into gneisses. Metamorphosed, gneiss like sedi- 

 ments, in which allothigenic minerals like feldspar are associated 

 with authigenic quartz and mica, and which are, to the author's 

 mind incorrectly, often designated gneiss, should be described 

 as gneissose greywacke, or as gneiss-greywacke. Some such 

 divisional line must be drawn if we are to obtain any enlighten- 

 ment on the structure and origin of districts composed of crystal- 

 line schists and massive rocks. Dubious schists should be 

 represented by a neutral colour, and not lumped in with the 

 gneisses. The designation gneiss is meaningless as long as 

 the most diversified crystalline and semi-crystalline schists are 

 included under it. 



Gneisses, to the author's mind, are granites possessing a 

 parallel structure, which is partly original, partly the result of 

 a more or less intense pressure during, or subsequent to, consoli- 

 dation. Whatever else may be said, gneisses and granites are 

 things that belong to the same category, and the author cannot 

 reconcile himself to their separation, with respect to origin. 



It cannot be natural to arrange in separate penological 

 categories eruptive granites and non-eruptive granites (gneisses), 

 eruptive diorites and non-eruptive diorites, eruptive gabbros and 

 non-eruptive gabbros, and to treat them from distinct points of 

 view. Plutonic rocks do not differ from the similarly com- 

 posed eruptive rocks, because they have not left the place in 

 which they were formed. 



How the origin of the plutonic rocks is to be conceived — 

 whether as the primordial terrestrial crust, or as produced by 

 the melting down or diagenesis of sediments, the latter supposi- 

 tion involving logically a similar origin for a part, at least, of 

 the eruptive rocks — are questions of which the answers are at 

 present less pressing, and which, with certitude, we shali probably 

 never solve. 



THE STRATIGRAPH1CAL SUCCESSION OF 

 THE CAMBRIAN FAUNAS IN NORTH 

 AMERICA. 1 



J\ REVIEW of the opinion of American geologists on the 



succession of the Cambrian faunas shows that all have 



followed the scheme published by Sir William Logan in 1855 



* Abstract of remarks made by Chas. B. Walcott, of the United States 

 Geological Survey, before the meeting of the International G< 

 Congress in London, in the course of discussion on the Cambrian System, 

 on September 18, 1888. 



(Geological Survey, Newfoundland), in placing the Para- 

 doxides fauna at the base, and then in succession the Olenellus 

 and Dicellocephalus or Olenus faunas. 



The discovery of Olatcllus Kicrulfi beneath the Paradoxides 

 zone in Sweden led me to re-examine the section of Cambrian 

 rocks in New York, and finally to go to Newfoundland. After 

 long search, I found a complete unbroken section on Manuel's 

 Brook, Conception Bay, that showed the following conformable 

 series : — 



Archrean Gneisses. 



1. Conglomerate resting unconformably upon a ... 



2. Sandstone, shale, and impure limestone with 



Olenellus Breggeri? and sixteen species of 

 the Olenellus fauna ... 



3. ( deenish argillaceous shale 



4- Red „ ,, 



5. Limestone 



0. Greenish argillaceous shales with an abundant 

 Paradoxides fauna at summit 



7. Dark argillaceous shales, Paradoxides, Micro- 



discus punciatus, Agraulus, Conocoryphe, 

 &c, &c, near base ... 



8. Alternating bands of shale and sandstone, with 



Orthis in great abundance ... 



35 



25 



4°- 



4 



Total 



270 



295 



400 



1071 



X. 



All strata unaltered and! 



Dip of strata, 12 to 15° 

 undisturbed. 



The above section proves that in North America, as in 

 Sweden, the Olenellus fauna is beneath the Paradoxides fauna. 

 This changes the American scheme of classification of the 

 Cambrian system, and places it in harmony with that of Europe. 

 The Olenellus fauna in America includes 42 genera and 112 

 species, and I now recall 4 genera and 20 species from Europe 

 not known in America, which give a fauna of 46 genera and 132 

 species beneath the Paradoxides zone. 



The following table exhibits the succession of the terranes as 

 now known in America : 



Table I. — Lower Silurian [Ordovician) System. 

 Subdivision. Terranes. Faunas. 



Upper Cambrian 



Middle Cambrian 



cs Lower Cambrian 



( Potsdam, Knox, 



< Tonto, Belle Isle, 

 ( &c. 



I St. John, 

 ■ Avalan, 

 ( Braintree. 

 1 Georgia, 



< Prospect, 



( Terra Nova. 



Dicellocephalus 

 or Olenus. 



Paradoxides. 



-Olenellus. 



A comparison of typical sections of the Cambrian system gives 

 the following : — 



Table II. 



Sweden. 



Wale 



Newfound- 

 land. 



Olenus zone. Olenus /one. Olenus zone. 



Xew York. 



Olenus zone. 



Paradoxides Paradoxides 

 /one. zone. 



Paradoxides 



Rocky 

 Mountains. 



Olem 



Olenellus 

 zone. 



Unknown. - 



Olenellus 

 zone. 



Represented by Represented 



other genera by other 



than Para- genera than 



doxides. Paradoxides. 



Olenellus /one. Olenellus zone 



It affords me pleasure to recognize the work of the Swedish 

 geologists, and to fully coincide with their results, and thus 

 firmly establish on the two continents the true order of 

 succession of the oldest known Palaeozoic fauna. 



1 Name proposed for new species of Olenellus. 

 After this paper was read, Prof. Lapworth showed me specimens of 

 Olenellus like O. BrSggeri, from Shropshire. 



