June 15, 1883.] 



SCIENCE. 



541 



ST. DAVID'S ROCKS AND UNIVERSAL 

 LAW. 



A DISCUSSION of the St. David's rocks has been 

 opened in the Geological society of London bj' Prof. 

 A. Geikle, director of the Geological survey of Great 

 Britain and Ireland, Tvhich possesses great interest to 

 all persons engaged in the study of the older crystal- 

 line rocks. The St. David's rocks, according to Dr. 

 Hicks, consist of three distinct pre-Cambrian forma- 

 tions in ascending order: the Dimetian, composed of 

 crystalline, gneissic. and granitoid rocks ; the sup- 

 posed unconformable Arvonian, formed of felsites, 

 quartz porjjhyries, halleflintas, etc. ; and thePebidian, 

 supposed to be unconformable to both the preced- 

 ing, and made up of tufas, volcanic breccias, and 

 basic lavas. The Cambrian is said to overlie all these, 

 and to have a basement conglomerate composed of 

 their ruins. 



Dr. Geikie maintains that the Dimetian is an erup- 

 tive granite, which has disrupted and altered the 

 Cambrian strata, even above the horizon of the sup- 

 posed basal conglomerate. Besides a pebbly quart- 

 zite formed of fragments torn from the Cambrian 

 conglomerate and greatly indurated, no rock, except 

 diabase, is found, according to him, in the granite 

 area; and this occurs throughout the entire district. 

 The granite cuts through successive horizons of the 

 Cambrian strata, and is younger than all of that for- 

 mation in the district. The Arvonian consists of 

 quartziferous porphyries, or elvans (associated with 

 the granite), and of the metamorphosed strata ad- 

 jacent. The Pebidian consists of a series of volcanic 

 tufas and breccias, with interstratiiied and intrusive 

 lavas. 



Geikie holds that the Pebidian is an integral part 

 of the Cambrian. It is cut by the Arvonian porphyry 

 and Dimetian granite, and is therefore older than 

 these. It is covered quite conformably by the Cam- 

 brian conglomerate, and not unconformably, as Hicks 

 claimed. Seams of tufa are interstratiiied at various 

 horizons in the conglomerate and strata above. This 

 Cambrian conglomerate, instead of being composed 

 of fragments of the Dimetian, Arvonian, and Pe- 

 bidian, consists almost entirely of quartz and quart- 

 zite; "only four per cent of fragments having been 

 found to have been derived from some of the project- 

 ing lava-islands underneath it.'' Professor Geikie 

 then claims that the names Dimetian, Arvonian, and 

 Pebidian " had been founded on an error of observa- 

 tion, and they ought to be dropped out of geological 

 literature." 



Prof. A. Renard also states that he had examined 

 these rocks microscopically, in concert with Drs. 

 Zirkel of Leipzig, and Wichmann of Utrecht; and 

 their conclusions are, that the so-called Dimetian 

 rock is unquestionably a true granite (eruptive). 

 The quartz porphyries were like the contact specimens 

 of granite, and believed to be such. The tufa found 

 in and above the conglomerate is a true tufa, and not 

 a mere superficial waste of older volcanic rocks. 

 The observed foliation existed above the conglomer- 

 ate as well as below. 



That the questions involved in Dr. Geikie's posi- 

 tion are deeply interesting, is manifest from the fact 

 that some fourteen persons joined in the discussions 

 which followed its statement. These questions are 

 of equal interest to American geologists and petrog- 

 raphers, since they are the same as those the present 

 writer lias raised regarding eastern Massachusetts, — 

 a district similar to St. David's, — also similar to 

 those raised by Professor Dana against the Taconian, 

 Montalban, and Huronian, in New England; by Dr. 



Selwyn, concerning the Norian, Montalban, and 

 Taconian, in Canada; by Messrs. Whitney, Selwyn, 

 Winchell, and Wadsworth, with respect to the Lake 

 Superior geology; and by Geikie and Wadsworth, re- 

 garding the Fortieth parallel exploration. 



The writer has nowhere seen any general state- 

 ment of the bearings of these questions; and it may 

 be briefly indicated here what some of them seem 

 to him to be. They seem to be involved in the dis- 

 tinction between one universal law, moving in a uni- 

 form, defiliite direction, and recurrent plienomena 

 or special creations and conditions. Under the lat- 

 ter view there seems to belong the belief that detri- 

 tal or chemical sediments are returned to eruptive 

 forms; that eruptive rocks are of chemical or sedi- 

 mentary origin; that these were different in pre-ter- 

 tiary time from what they were in the tertiary; that 

 certain geological periods are marked by certain liinds 

 of rock ; that the azoic system has been subdivided 

 upon natural principles ; that there have been recur- 

 rent periods of heat and cold. This view includes the 

 theory of the metamorphic origin of granite, the pres- 

 ent geologico-mineralogical classification of rocks, 

 and embraces uniformitarlanism, catastrophism, plu- 

 tonism, and neptunism. 



The other maintains the existence of a universal 

 law, which should be the guide in all investigations, 

 — a law, which, in its more special applications. Pro- 

 fessor Whitney has endeavored to illustrate in his 

 Climatic changes, and Sir William Thomson in his 

 papers on the age of the earth and sun, — a law 

 which the present writer has tried to express in his 

 petrographical work. It is regarded as the law which 

 will one day be completely worked out, and in accord- 

 ance with which our views in history, philosophy, 

 science, — all branches of human knowledge, — will 

 then be reconstructed. The expression of the law 

 varies in different ages, but for the physical universe 

 it seems best formulated at the present time by Sir 

 William Thomson : The degradation and dissipation 

 of energy, the passage from the unstable towards a 

 more stable condition, tlie tendency to harmonize 

 with the environment, — the law under which the 

 universe has moved from the beginning, and under 

 which it will continue its course uniformly towards 

 the end; it assumes that no turning-back; can occur, 

 and that no energy once lost can be restored, except 

 by the same Almighty Power which gave it birth. 



M. E. Wadsworth. 



THK HUMAN REMAINS OF THE BONE- 

 CAVERNS OF BRAZIL. 



The discovery by the late Dr. Lund of human re- 

 mains associated with the extinct mammalian fauna 

 of the caverns of Lagoa Santa in the province of 

 Minas Geraes, Brazil, made famous by his researches, 

 has, until recently, passed almost unnoticed among 

 ethnologists. Dr. Lund's statements in the communi- 

 cations which accompanied the human bones, sent to 

 the societies of Rio de Janeiro and Copenhagen, are, I 

 believe (I write without the documents for reference), 

 unqualified as to the direct association of the human 

 with the extinct mammalian remains, and have been 

 received as conclusive by prominent ethnologists. 

 There can be no question of Dr. Lund's perfect good 

 faith in the matter; but it may be asked whether, 

 forty years ago, such care as is now considered neces- 

 sary in such investigations would have been exer- 

 cised, even by so able and conscientious an observer 

 as Lund is recognized to have been. 



So long a time has elapsed, that it is now diflBcult 

 to verify the exact conditions under which the bones 



