May 9, 1 87 2 J 



NATURE 



anj it was soon made apparent tliat the genus ParadoxiJes, both 

 here and in North Wales, was confined to a horizon below the 

 great miss of the Lingula flags, which, on the contrary, are 

 characterised by numerous species of OUniis. These lower or 

 Menevian beds are hence regarded by Salter as equivalent to 

 the lowest pjition of the Etage C of Birrande. 



Beneath these Menevian beds there lies, in apparent cjnformity, 

 the great Lower Cambrian series, frequently called the bottom 

 or basement rocks by the Government surveyors ; representei 

 in North Wales by the Harlech grits, and in South Wales, near 

 St. IJavid's, by a similar series of green and purple sandstones, 

 considered by Murchison and by others as the equivalent of the 

 Harlech rocks. They were still supposed to be unfossiliferous 

 until, in June 1S67, Salter and Hicks announced the discovery in 

 the red beds of this lower series, at .St. David's, of a Liiv^iilella, 

 very like L. fernt^^iiita of the Menevian (Geol. Jour. x.\iii. 339 ; 

 Siluri.a, 4th ed. Sj^)' This led to a further examination of these 

 Lower Cambrian beds, which has resulted in the discovery in them 

 of a fauna distinctly primordial in type, and linked by the 

 presence of several identical fossils to the Menevian ; but in 

 many respects distinct, and marking a lower fossiliferous horizon 

 than anything known in Bohemia or in Scandinavia. 



The first announcement of these important results was made 

 to the British Association at Norwich in 1868. Further details 

 were, however, laid before the Geological Society in I\Lay 1871 

 by Messrs. Harkness and Hicks, whose paper on the Ancient 

 Rocks of St. David's Promontory appears in the' Geological 

 Journal for November 1 87 1 (xxviii. 384). The Cambrian 

 sediments here rest upon an older series of crystalline stratified 

 rocks, describeil by the geological surveyors as syenite and 

 greenstone, and having a north-west strike. Lying unconform- 

 ably upon these, and with a north-east strike, we have the follow- 

 ing series, in ascendhig order : — I, quartzose conglomerate, 60ft. ; 

 2, greenish flaggy sandstone, 460ft. ; 3, red Hags or slaty beds, 

 50ft., containing /.inxiilel/a fiyyuginea, besides a larger species, 

 Disciut!, and Li-ptTtlilia caml/rcnsis ; 4, .purple and greenish 

 sandstones, i, 000ft. ; 5, yellowish gray sandstones, flags and 

 shales, 150ft. .with Plutonia, Conxoiyp/u\ Microdistiis, Agiwsliis, 

 T/ura, and Pn>tos/>,oi!;^ia ; 6, gray, purple and red flaggy sand- 

 stones, with most of the above genera, 1,500ft. ; 7, gray flaggy 

 beds, l5o!'t., with Pam/oxides ; 8, true Menevian beds, richly 

 fossiliferous, 500ft. The latter are the probable equivalent of 

 the base of Barrande's Etage C, and at St. David's are con- 

 formably overlain by the Lingula flags, beneath which we have, 

 including the Menevi.an, a conformable series of 3,370ft. of un- 

 crystalline sediments, fossiliferous nearly to the base, and holding 

 a well-marked fauna distinct from anything hitherto known in 

 Great Britain or elsewhere. 



The Menevian beds are connected with the underlying strata 

 by the presence of Lini;iildla femii^inea, Discina pilcoliis, and 

 Obolclla sa^ittalHs, which extend through the whole series ; and 

 also by the genus Pamdoxidis, four species of which occur in 

 the lower strata, from wliicli the genus Olcniis, which characterises 

 the Lingula flags, seems to be absent. To a large tuberculated 

 trilobite of a new genus found in these lowest rocks the name of 

 Plutonia Scdg^-XHckii has been given. Hicks has jiroposed to uni'e 

 the Menevian with the Harlech beds, and to make the summit 

 of the former the dividing line between the Lower and Middle 

 Cambrian, a suggestion which has been adopted by Lyell. 

 (Proc Brit. Assoc, for 1868, p. 68, and Lyell, Student's Manual 

 of Geology, 466 — 469.) 



Both Phillips and Lyell give the name of Upper Cambrian 

 to the Lingula fl.igs and the Tremadoc slate;, which together 

 constitute the Middle Cambrian of Sedgwick, and concede the 

 title of Lower Sdurian to the Bala group or Upper Cambrian of 

 Sedgwick. The same view is adopted by Linnarsson in Sweden, 

 who places the line between Cambrian and Silurian at the base 

 of the Llandeilo or the second fauna. It was by following these 

 authorities that I, inadvertently, in my address to the American 

 Association for the Advancement of Science in August 1871, 

 gave this horizon as the original division between Cambrian and 

 Silurian. The reader of the first part of tliis paper will see with 

 how much justice Sedgwick claims for the Cambrian the whole 

 of the fossiliferous rocks of Wales beneath the base of the May 

 Hill sandstone, including both the first and the second fauna. I 

 cannot but agree with the late Henry Darwin Rogers, who, in 

 1856, reserved the designation of " the true European Silurian" 

 for the rocks nbcrve this horizon. (Keith Johnston's Physical 

 Atlas, 2nd ed. ) 



T. Sterry Hunt 

 (7y be continued) 



ACOUSTICAL EXPERIMENTS* 

 Showing th.vf the Tr.\nsi,,\tiox of a Virrating Body 



CAUSES IT TO GIVE A WaVE-LEVGTH DIFFERING FROM 



that produced by the same vibrating body when 

 Stationary 



The Apparatus 



pOUR tuning-forks mounted on resonant cases and giving the 

 note UT', ^ 256 complete vibrations per second, were o'j- 

 tained. I will designate them as Nos. I, 2, 3, and 4. 



Nos. I and 2 were brought into perfect unison by a process to 

 be described. 



No. I was placed before a lantern, ani just touching one of 

 its prongs was a small bail {5 or 6™'" diam.) of good cork, sus- 

 pended by a silk fib'e. The images of the fork and of the cork 

 ball were projecteil on a screen. 



No. 3 had one prong weighted with wax, so that it gave twj 

 beats a second with No. I or 2. 



No. 4 had the ends of its prongs filed off, until it also gave 

 two beats per second with I or 2 ; thus No. 4 gave two vibra- 

 tions a second more than No. i, while fork No. 3 gave two 

 vibrations a second less than No. i. 



The Experiments 



\\\ the exiieriments one to seven inclusive, fork No. I remains 

 before the lantern, with the suspended cork ball just touching 

 one of its prongs. 



E.xi'. I. Fork No. 2, screwed on its case, was held in the 

 hand, at a distance of 30 to 5o ft. from No. i, and sounded ; the 

 ball was projected from the prong of fork i, which vibrated in 

 unison with 2. 



E.XP. 2. I stationed myself 30 ft. distant from fork No. I, and 

 fork No. 2 was screwed off its case and vibrated in one hand, 

 while the case was held in the other. I now walked rapidly 

 toward fork i, and after I was in regular motion I placed the 

 fork on its case, and just before I ceased walking I took it off ; 

 although, when I did so, I was only about a foot froai fork I, 

 yet the cork ball remained at rest against its prong. 



E.\i'. 3. Again I walked toward i, as in Exp. 2, but I did not 

 remove the fork from its case after it was placed on it. The 

 ball remained at rest until the moment I suddenly stopped 

 walking ; at that instant the ball flew from the fork, while an 

 assistant, whose ear was close to the case of fork I, while his 

 eye was directed to the screen, found that at the instant I stopped 

 walking, the fork i sounded, while the ball jumped from its 

 prong. 



E.xi'S. 4 and 5. These experiments were exactly like Exps. 

 2 and 3, except that I walked away from fork I instead of 

 approaching it. The results vifere the same as in Exps. 2 

 and 3. 



Exr. 6. Fork No. 3, giving 254 vibrations per second, was 

 sounded as in Exp. I. It had no effect in moving the ball. I 

 now screwed the fork off its case, and, standing about 30 ft. 

 from fork I, with my arm I swung the case toward fork i, and 

 while it was approaching it I placed fork No. 3 on the case ; 

 the proper velocity (from eight to nine feet per second) having 

 been obtained, the ball was suddenly projected from fork i. 

 On greatly increasing or decreasing the above velocity of the 

 moving case, the vibrations of fork 3 produced no elfect on 

 fork I. 



E.XP. 7. Fork No. 4, which gives two vibrations per second 

 more than No. i, was substituted in Exp. 6, but was placed on 

 its swinging case when this was receding from fork I. The 

 effect of this motion and of varying velocities was the same as 

 in Exp. 6. 



Exr. 8. I placed fork 3 before the lantern, and swung fork 

 I as in Exp. 7. The effects were the same as described in 

 Exp. 7. 



E.xr. g. I now placed fork 4 before the lantern, and moved 

 fork I as in Exp. 6. The effect on the ball was the same as in 

 Ex[>. 6. 



By these simple experiments I have shown the change of 

 wave-length produced by the translation of the vibrating body, 

 and have given an experimental proof of the important theorem 

 which Doppler established in 1841. By analogy they clearly 

 unfold that exquisite modern method of determining the motions 



' By Alfred M. Mayer, Ph.D., Professor ofPhysics in the Slevens In- 

 stitute of Technology, Hoboken, New Jersey (reprirued from the America/t 

 'journal of Science and Arts, vol. iii.,April, 1872). 



