358 



GEOLOGY IN AMERICA. 



[1855. 



of any one to roam over otlier,?' territoriea, lest he ignorantly gather 

 for you noxious weeds. I have, therefore, chosen to confine myself to 

 a single topic — that of Geology, and I propose, instead of simply re- 

 vievvin"' recent geological papers, to restrict myself to some of the gen- 

 eral conclusions that flow from the researches of American Geologists, 

 and the bearings of the facts or conclusions on geological science. 



I shall touch briefly on the several topics, as it is a subject that 

 would more easily be brought into the compass of six hours than one. 

 In drawing conclusions among conflicting opinions, or on points where 

 no opinion has been expressed, I shall endeavour to treat the subject 

 and the views of others in all fairness, and shall be satisfied if those 

 who differ from me shall acknowledge that I have honestly sought the 

 truth. 



In the first place, we should have a clear apprehension of the intent 

 or aim of Geological Science. It has been often said that geology is a his- 

 tory, the records of which are in the rocks ; and such is its highest de- 

 partment. But is this clearly appreciated ? If so, why do we find 

 text-books, even the highest in authority in the English language, 

 written back-end foremost — like a history of England commencing with 

 the reign of Victoria ? In history, the phases of every age are deeply 

 rooted in the preceding and intimately dependent on the whole past ; 

 there is a literal unfolding of events as time moves on, and this is emi- 

 nently true of geology. 



Geology is not simply the science of rocks ; for rocks are but inci- 

 dents in the earth's history, and may or may not have been the same iu 

 distant places. It has its more exalted end —even the study of the 

 progress of life from its earliest dawn to the appearance of man ; and 

 instead of saying that fossils are of use to determine rocks, we should 

 rather say that rocks are of use for the display of the succession of 

 fossils. Both statements are correct, but the latter is the fundamental 

 truth of the science. 



From the progress of life geological time derives its division into 

 Ages, as has been so beautifully exhibited by Agassiz. The successive 

 phases in the progress of life are the great steps in the earth's history. 

 What if in one country the rocks make a consecutive series without any 

 marked interruption between two of these great ages, while there is a 

 break, or convenient starting-point, in another ? Does this alter the 

 actuality of the ages ? It is only like a book without chapters, in one 

 case, and with arbitrary sections in another ? Again, what if the events 

 characteristic of an age, that is, in geology, the races of plants or ani- 

 mals — appear to some extent in the preceding and following ages, so 

 that they thus blend with one another ? It is but an illustration of the 

 principle just stated, that Tmie is One — ages have their progressive 

 developement, flowing partly out of earlier time, and casting their 

 lights and shadows into the far future. We thus distinguish the ages 

 by the culmination of their great characteristics, as we would mark a 

 wave by its crest. 



Divisions of time suhordmate to the great ages will necessarily depend 

 on revolutions in the earth's surface, marked by an abrupt transition 

 either in the organic remains of the region, or in the succession of 

 rocks. Such divisions are not universal. Each continent has its own 

 periods and epochs, and the geologists of New York and other States 

 have wisely recognized this fact — disregarding European stages or 

 subdivisions. This is as true a principle for the cretaceous and terti- 

 ary, as for the Silurian and Devonian. The usurpation of Cromwell 

 made an epoch in English annals — not in the French or Chinese. We 

 should study carefully the records before admitting that any physical 

 event in America was contemporaneous with one in Europe. The 

 unity in geological history is in the progress of life, and in the great 

 physical causes of change — not in the succession of rocks. 



The Geological Ages, as laid down by Agassiz, are the following : — 

 I. The Affe of Fishes — including the Silurian and Devonian. 11. The 

 Affe of Sepiiles — embracing from the Carboniferous through the Creta- 

 ceous. III. The Affe of Mammals, or the Tertiary and Post-Tertiary. 

 IV. The.4i7c of Man, or the recent evs^— fishes being regarded as the 

 highest and characteristic race of the first age, reptiles of the second, 

 and mammals of the third. 



More recent researches abroad, and also the investigations of Mr. 

 Hall in this country, have shown that the supposed fish remains of the 

 Silurian are probably fragments of Crustacea, if we except those of 

 certain beds near the top of the Silurian ; and hence the Age of Fishes 

 properly begins with the Devonian. What, then, is the Silurian ? It 

 is pre-eminently the Aqe of Molluscs. 



tlnlike the other two Invertebrate Sub-kingdoms — the Radiate and 

 Articulate, which also appear in the earliest fossiliferous beds — the 

 MoUuscan Sub-kingdom is brought out in all its grander divisions. 

 There is not simply the type, but the type analyzed or unfolded in its 



several departments from the Brachiopods and Bryozoa up to the high- 

 est group of all — the Cephalopods. And among these Cephalopoda, 

 although they may have beeu inferior in grade to some of later periods, 

 there were species of gigantic size — the shell reaching the length of ten 

 or twelve feet. The Silurian is, therefore, most appropriately styled 

 the MoLLusoAN Age. 



Tlie Paloiozoic Tribolites were the lowest among Crustacea, and 

 Crustacea rank low among Articulates ; moreover, Crustacea (and the 

 Articulata iu general) did not reach their fullest development until the 

 Human Era. 



The Radiata were well represented in the Silurian periods, but, while 

 inferior to the MoUusca as a Sub-kingdom, only the Corals and Crinoida 

 — the lower fixed or vegetable species — with rare exceptions, occur in 

 the Silurian or Molluscau Age. 



Viewing the history, then, zoologically, the ages are, the Age of 

 Molluscs — of Fishes — of Reptiles — of Mammals — of Man. 



We may now change the point of view to the Vegetable Kingdom. 

 The ages thence indicated would be three : — 



I. The Age ofAlgce or Marine Plants — corresponding to the Silurian 

 and Devonian. 



II. The Affe of Acrogens, or Flowerless Trees — that is, the Leptdo- 

 dendra, Sigillaricc, and Calamites — corresponding to the Coal Period 

 and the Permian — a name first proposed by Brongniart, and which may 

 still be retained, as it is far from certain that the SigUlarias and Cala- 

 mites are most nearly related to the Coniferm. 



III. The Age of Angiosperms, or our common trees — like the oak, 

 elm, &c. — beginning with the Tertiary. 



The interval between the second and third of these ages is occupied 

 mainly by Couiferaj, the pine tribe, and Cycadete, the true Gymno- 

 sperms, species of which were abundant in the Coal period, and have 

 continued common ever since. The Coniferce, in the simplicity of their 

 flowers and their naked seeds, are next akin to the Acrogens, or flower- 

 less trees. Although in the main a flowerless vegetation — for the sup- 

 posed remains of flowers observed abroad have been recently referred to 

 undeveloped leaf buds — it appears from the observations of Dr. New- 

 berry, that there were true flowers over the Ohio prairies, apparently 

 monocotylediuous, and related to the lily tribe. But no palms or mo- 

 nocotyledinous trees have been found here. 



Combining the results from the Animal and Vegetable Kingdoms, we 

 should introduce the age of Acrogens, for the Coal period and Permian 

 between the age of Fishes and the age of Pieptiles — a space in time 

 zoologically occupied by the overlapping of these two ages. 



The order then reads : the age of Molluscs, of Fishes, of Acrogens 

 or Coal Plants, of Rejjtiles, of Mammals, of Man. 



The limits of these ages are as distinct as History admits of; their 

 blendings where they Join, and the incipient appearance of a type be ■ 

 fore the age it afterward characterizes fully opens, are in accordance 

 with principles already explained. 



The reality of progress from lower to higher forms is not more 

 strongly marked in these names properly applied than in the rocks. If 

 hereafter mammals, reptiles, or fishes are found a little lower than now 

 known, it will be changing but a sentence in the history, not the grand 

 idea which pervades it. 



A theory lately broached by one whose recent death has caused uni- 

 versal grief to science, supposes that the Reptilian was an age of dimi- 

 nislied life between the two extremes in time — the PalaDozoic and Mam- 

 malian ages. But in fact, two grand divisions of animals, the MoUus- 

 can and Reptilian, at this time reach their climax and begin their de- 

 cline, and this is the earliest instance of the highest culmination of a 

 grand zoological type, ■ ^ 



Preceding the Silurian of Molluscan Age, there is the Azoic Age, or 

 age without animal life. It was so named by Murchison and De Ver- 

 neuil, and first recognised in its full importance and formally announced 

 in this country in the Geological Report of Messrs. Foster and Whitney, 

 although previously admitted as a general fact by most geologists. 



It embraces all the lowest rocks up to the Silurian, for much of the 

 lowest granite cannot be excluded. The actual absence of animal life 

 in the so-called Azoic Age in this country is rendered highly probable, 

 as Foster and Whitney show, by the fact that many of the rocks are 

 slates and sandstones, like fossiliferous Silurian rocks, and yet have no 

 fossils ; and, moreover, the beds on this continent were uplifted and 

 folded, and to a gi-eat extont crystallized on a vast scale, before the 

 first Silurian layers were ".eposited. A grand revolution is here indi- 

 cated, apparently the closing event of the early physical history of the 

 globe. As plants may live in water too Iiot or impure for animals, and 

 moreover since all nature exemplifies the principle that the earth's 

 surface was occupied with life as soon as fitted, and with the highes 



