pebbles cemented n-ith mhite limestone, ancl gracl- that the mhole of the old becl is to some extent 1,er- nally changing upmarcl into a firm, barren, homoge- meatecl by the vatels of the unclergro~mclriver.- neous limestone. The extent and direction of this unclergro~~ncl This formation mas in continuation of, or some- channel, and the determination of other streams times below, the horizon of the Exogyra arietina than the Blanco which may be tapped by it, are marl. Here, then, mas the solution of the problem promising subjects of future investigation, which I of the San XIarcos. The rocks before me were of hope at an early clate to unclertake, not only in the the later cretaceous, deposited upon the gravel and hope of gaining, by a stuclp of the amount of erosion shingle -which had formecl the bed of a river during of the older rocks, some idea of the duration of the the period of emergence. They had choked up and interval betmeen the tmo periods of rock formation, rendered impervious the superficial layers of the but of obtaining some inforination concerniug the river-bed, but doubtless left the loner gravel and fresh-mater life of that period. EDTVIKJ. POND. sand beds in as gooil condition for carrying water as Austin. Tex., Nay 18. ever. To make the ericlence comolete. I found, on examination of the rock ma, whiih lies only a few Electrical phenomena at the Washington feet above the river, that it is the Soft limestone of the later cretaceous, containing numerous specimens monument. of Gryphaea laeviuscnla R., -- a fossil found in great In various numbers of Science of recent dates abundance a short distance east ancl north of Austin, have appeared notices of certain electrical phe- ancl there occurring at the top of the Austin lime- nomena experienced on mestern mountain-peaks. stone. The peculiar effects experienced consist in general We have, then, the channel, and need only to ac- of a hissing or crackling sound accompanying single count for the water to fill it. The Blanco River, in discharges, or a continuons flow of sparks, and the a westerly direction fro111 San lIarcos, is about fif- characteristic tingling sensation vhen a finger is teen miles distant. In the upper part of its course presented to any metallic object near by. These es- it is a running streanl of considerable rolnme ; but periences, despite the common belief, are not rare,

SECT104 OF CRET.iCEOUB ROCKS AT BAN IIARCOS, HATS CODSTT, TEX., LOOKIXG SODTH. DDD, principal springs : B, hill upon ~hichis the Chautauqua assembly building; na, later cretaceous limestone, mith Exogyra laeviuscula R.; bb, Exogyra arietina marl: cc, flrm limestone, with Terebratula JTacoensis R. and Pecten quadricostatuj Somerhy ; passing ilito ad. thin-bedded soft linlestoue, ~ithOstrea carillaba Lam ancl numerous fossils of tsues Ostrea, Gryphaea, Turritella, Pecten, Cardium, Cypricardia, Trigonia, Tosaster, and -4mnlonites: ee, hard but-bmken lirneatone, ~lthCapriuas. below the point mest of San llarcos it loses size nor confined to certain persons. At Pike's Pealr rapidly, and at the point mhere the International ancl these electrical nianifestations are of frequent oc- great northern railroacl croshes it, and below, it is cnrrence, and a list hai been pnblished (Report of for the greater part of the year only a clry bed with chief siy~iciloficev, 1882, p. 893) shon~ingthe ac- occasional pools of standing vater. companying meteorological conditions in fifty-six It has evidently cut through the overlying de- instances, and proving that these electrical phe- posits, till it has reached the ancient becl of the San nomena are closely connected with the occurrence Marcos, vhich, thns filled mith mater, has been of hail, snow, ancl thunder-storms. At these times enabled to clear an7ay n-haterer later deposits lay it is easy to obtain sparks from moollen or fur gar- upon its ancient becl back to the present source of ments, anci to recei~e shocks on opening the door of the San 3larcos River. the store, or touching any metallic bocly. Again, at To a geologist the question -would at once occnr, Fort St. llichael's (Ibid., 1881, 11. 768) during the TT7hy has not the current opened the nhole of the coldest meather of winter, and alx-aye after a snov old bed, ancl so caused the abandonment of the fog, " the air is so electrified that the hair upon any present bed of the Blanco long ago? The ans-ver loose fur stands up, and a spark can be dmmn b~- lies in the confignration of the older cretaceous presenting a finger to the tip of a single hair." strata at its present source. The old river had cut In all these cases the observer may be considered under what mas the overhanging cliff of the hard as an insulated (perhaps, as in the case of one of yo111 limestone cc, causing it to dip abruptl~; as repre- correspondents, he may stand upon a thick woollen sented in above section, and then founrl the least Na~ajoblanket) bocly, n-hich, because of the electri- resi~tancein cutting a channel from the softer Ostrea fication of the air, acquiles a charge. Contact mith carinata bed rather than in carrying away the fallen a body, in better, although perhaps not very good, mass of the harder limestone. Hence the rocks of conneclion with the ground, results in a discharge, the old river-bed proper, at uct, though very soft, mi& the described effects, varying in intensity x-ith are protected from fnrther erosion from beneath by the degree of electrification. This condition of the stratum cc. things is in part, I think, imitatecl in some esperi- There are, however, small springs at s, which show nlents I hal-e lliacle at the top of the JTTashington [VOL. IX., NO. 226 monument, during thunder-storms. The appnratus and repeat the same operation mith the next light- used consists of a large insulated collector, a mocli- ning-flnsh. ALEXANDERMCADIE. fied Mascart electrometer, and Mascart insulators Cambridge, May 25. and the necessary adjuncts. As the thunder-clouds appronch, the electrometer-needle becomes very ac- tive, and, after considernble oscillation, begins to Railway jubilee, Paris, 1887. move stenclily in one direction (generally negative). I am requested by the executive cornmittee in until a deflection indicating, for example, a potential Paris to ask the favor of nppealing through your of three thousand volts, is reached. when, simultane- col~~mnsfor the loan of any objects, books, medals, ous mith a flash of lightning, occurs a quick drop to dralvings, etc., relating to the history of railways, zero, to begin again slowly to increase, and then and means of transportation generally, both ancient more rapidly, until the next flash of lightning. So and modern, in this country. perfect is this correspondence, that the lightning can I am directed, also, to sny thnt nll expenses of be tillled ns nccurately fronz the indications of the for~~arclingand returning the same to the lenders, electrometer as by direct vision. If at this time a packing and nnpaclring, mill be defrayed by the ex- finger be held out towards the collector, spnrks nre ecutive, that each object will be insured for the given, vith the accolnpanying crackling and hissing, value the lender may pnt npon it, nnd thnt special and the tingling sensation in the finger. In such a attendants vill be tolcl off for their safe custody. case, the observer is simply gionnding the insulated A11 communications on the subject ]nay be ad- charged collector. The greatest spnrking distance, dressed to &I. CT. Senechal, 8 Faubourg Montmnrtre, in our experience thus far, as determined by direct Paris, or to Mr. George L. Fov-ley, M.E. (of New mensurement, mas n l~ttleunder four millimetres. Porlr Cit,y), conliuissioner in charge for the United I have never found any difference (as one of your States, Palnis de l'Exposition, Bois de Vincennes. oorresponclents intimates) in the spnrking distance, Paris, France. By nddressing colnmunications depending on the finger. The potential of the air, direct to Paris, much vnlnable time trill be snved. however, as shown by the electrometer readings, is JOHSW. WESTON. constantly fluctuating, often very rapidly, and at Chicago, Ill., May 23. certain times the potential of the air is zero. Of course, n finger presented at such a time, fails to The maxillo-palatines of Tachycineta. draw a spark. With iespect to nhnt your correspondent says in To imitate more closely the conditions of the regard to a cliaming of mine, I cnn only sny that the monntnin-side, the previous ariangerllellt mns re- sbnll of T. thnlnssina from ~rhichit was made is a versed, and the ol>serverinsulated by standing on a perfect one, and my copy corre~tin a11 particulars. Navnjo blanket fol(1ed several times. This 1s but This is more than I call say for the reproclnction of poor insulation, though it ansmere~lthe purpose. it (Scie~~ce.No. 223, fig. 1); but ho~veverthis mny Standing close to the open win~lo\vof the monument, be, it at leabt affords me nov the opportunity to the results mere as nnticipnted. My hair stood on yield gracefully to my cr~tic,for I nm free to confess end, aid, on presenting a linuclrle to the iron frame- that the n~~xillo-pnlatinesof that skull are ' inl- work, n spaik passed. I should renlnrlc that these perfect ' nncl 'broken off ' -on paper -- by Mr. F. effects mere only esperiencecl during a thi~ncler- A. Lucas; as any one nlaj see TV~Ocares to compare stonu. I tried the expelinlent at other times, with- VIT, drawine in the Proceedinns of the Zoiilo~ical 071t success. s;ciety of ~%ndon(Dee. 1, 188< 11. 899, fig. 3') kith There are tnTofurther points of interest to nhich his copy of ~t in Scie~lce,to ~vhichI refer above. attention is called. Professor LeConte has insta~lced R. W. SHUFELDT. (Science, ix. No. 205) the case of the survey party on Fort Kingate, R.Jles., May 20 one of the Man Juan mountains, vhere " a sudden ces- sation of the distressing electrical effects was experi- enced vhene~~erthere occurred a flash of lightning." No parietal foramen in Tritylodon. This is confirmed by what precedes: and 0111- elec- Dr. George Banr of the Peabody museum, New trometer readings make it certain that every light- Hayen, has been recently studying the fossil verte- ning-flash relieves the electrical tension, ancl givesns brates in the British muse~unof natural history. At also the means of estimating the electromotive force my request he has ltindly made a careful study of producing the disruptive discharge, and the electric the sliull of Tritylodon, and finds that Professor strength of the air, nnder nataml conditions. The Omen's observation of a forallleu between the parie- necond point of interest is the effect of electrifica- tal l~onesis incorrect. He writes (London, May S), tion upon the water-particles present. LordRayleigh 'bIch habe Tritylodon hier genan nntersucht, ein has shonm horn the chnsacter and direc,tion of a fine Parietal-Foranlea esistirt ~zicl~t; es ist ~venigstens stream of water niay be altered by electrical in- Beine Spur desselben naChT~eisbar." This contra- fluences ; for exanlple, a stick of sealing-wax, when dicts, without question, the suggestion I lllade in a rubbed, distorting a fine jet of water. Effects of the recent number of Sczozce, upon the strength of Pro- same character I noticed in the jet of m-ater issuing fessor Owen's observntion, that there mas probably a from the nozzle of the collector. Vhen the collector pineal eye of considerable size in Tritylodon. I was ' gronndecl,' the st>realllwoalcl preserve a certain hasten to lnalie the correction, before the snggestion even, rounded character, breaking into drops some goes any further. Althongh it has proved incorrect, four inches awax from the place of issue. Remov- I thinli any one nho mill exallline Professor Owen's ing the ground connection, the streail1 IT-oulcltwist figure and description of the Tritylodonsk~ill(Quart. and split into sprays with the increasing electrifica- jotcr.ls, yeol. soc., 1884) will admit that there was suf- tion. Sirnnltaneous nrith a fiash of lightning, this ficient ground for this conjecture. distortion ceased, and for the ll~olilentthe stream HENRYF. OSBORN. resumed its firat character, only to be again distorted, Princeton, X.J., Xay 26.