two days, no sensible error would be introduced by interpolating between the numbers for the days immediately preceding and following the omitted days. The years selected for this examination were 1850, 1851, 1852, 1868, 1869, 1870; and the beginning of the first period in each year after the first was thus found:-Fourteen periods of 26 days each amount to 3682 days. For convenience, after completion of the annual winter adjustments, the first period in 1850 was made to commence on January 17; therefore the first period in 1851 was commenced on January 21, and that in 1852 on January 25. Similarly, the first periods in 1868, 1869, 1870 commenced on January 1, 4, and 8 respectively; and the beginnings in the three later years are not unconnected with those in the three earlier years: for, from 1852, January 25, to 1868, January 1, are 5820 days, and 221 periods of 26 days each are 58193 days; but as the years are widely separated, and a small error of period would produce a large discordance, it has appeared best to exhibit the results of the two three-years' groups separately. Some periods, in which there were unusually large interruptions, or which were partly occupied with experiments, were omitted entirely. The following is a complete list of periods omitted:-In 1850, that beginning with December 24 for horizontal force; in 1851, that beginning with March 14 for western declination, and those beginning with March 14, June 28, July 24, for horizontal force; in 1852, those beginning with February 20, May 9, December 6, for both elements; in 1868, those beginning with February 23 for declination, and January 1, January 27, February 23, and December 8 for horizontal force; in 1869, those beginning with October 21 and December 12 for both elements; and in 1870, those beginning with June 15 and December 16 for declination, and that beginning with December 16 for horizontal force. Interpolations of three days occur only in the following instances:-1850, (dec.) Feb. 4-6, (h. f.) Feb. 9-11, July 23-25; 1851, (dec.) Feb. 18-20, Oct. 20-22, (h. f.) June 9-11; 1852, (dec.) Feb. 7-9; 1868, (dec.) Feb. 15-17, (h. f.) none; 1869, (dec.) June 6-8, (h. f.) June 6-8; 1870, (dec.) Sept. 24-26, (h. f.) Sept. 24-26. The mean values of each element for each progressive day in every period of the several years, uncorrected for the proportional part of secular change through the 26 days, and omitting the imperfect 27th day, are as follows : Taking the means of these numbers separately for the groups of years 1850-1852 and 1868-1870, and applying the proportional parts of secular correction, at the rate of +0'62 for 26 days in western declination, and at the rate of zontal force, we have the following results : 00013 for 26 days in hori 144 Royal Society:-The Astronomer Royal on a supposed 823 Western Declination (omitting 22° 10′ in the first range of years, and 20° in the second). 1850 9-839-70 9-88 9-859-589-74 970 959 9-71 9979-83 10-15 10-07 9-91 4.10 3.95 3.72 3.95 3.74 3.89 4.28 9.99 9-849-969-789-88 10-04 10-24 10-16 10-15 10-06 10-25 10-29 3.93 4.03 3.75 3.82 3.72 3-82 3.93 4:00 4.04 3.88 3.92 3.70 3.97 3.97 4.02 4.03 3-86 4.00 4.13 Horizontal Force (omitting 11300 in the first range of years, and 14400 in the second). 83 75 72 The mean for declination in 1870 and, still more remarkably, the mean for horizontal force in 1870 appear to exhibit an increase Dr. Hornstein's investigation was limited to observations made in 1870. Postscript. Received May 9, 1872. As the diurnal changes of the magnetic elements appear to be due to the action of the sun, it seemed probable that any irregularity in that action depending on the face of the sun presented to the earth might be principally conspicuous in the diurnal change. I therefore thought it prudent to avail myself of the computations of diurnal change of western declination already prepared at the Royal ObservaThe following numbers have been computed in exactly the same manner as those for absolute western declination. tory. Periodicity in Terrestrial Magnetism. 1830. 12-16 13-01 14:14 12-69 11-29 11.94 13-60 10-32 12-21 13:33 11.89 12-63 12-81 12-84 12-55 13.11) 13.06 13-23 14:04 1831. 11-83 10:59 10-96 11-21 11:45 13-75 10-99 13-14 12-82 12-31 11-23 11-92 12-92 13-15 11-04 13-27 11-62 10:41 11:31 1852. 12:25 14.95 14-65 14:52 12-08 11-66 13-15 14:35 15-73 12-82 14-16 13:47 | 13-82 | 14′43| 13·45 | 15′15 | 12:43 | 14:59 1468 1850- 12-08 1852. 145 1868. 9-70 10-28 11-00 11-02 12-22 11-58 11:39 10-C8 11-89 12-14 11-86 13:45 12:58 12-78 13-95 11:45 13:47 15-36 13-75 11-09 10:05 11-01 10-30 10-62 10-25 10:35 1869. 11:46 11-61 11-55 13:58 12-93 14:49 12-87 13-09 13:30 14:32 13-78 14-03 14-81 14-18 14-03 14-28 13-09 13.93 14-28 14:13 12-68 11-72 12-68 12:42 13-33 12-53 16:01 14-93 15-24 15:23 13.88 15-19 15:48 16:09 15:31 14.91 14-03 13-70 15-02 14:49 13-07 14-70 14-27 13:48 16-25 15:40 15-99 15-87 16-06 15:12 16:43 15-39 1870. 1968- } 1870. 12-95 12:41 12-89 13-65 12.89 14.38 13-64 13-99 14-19 13-56 13-76 14:36 14:53 13-25 12:38 13:33 12:55 12-68 13-59 13-29 12-79 12-62 13-25 12-85 13-99 13-17. In 1870, the diurnal change appears to be less from the 10th to the small. In 1869 it appears to be larger at the same part of the period. the period. 18th day than in other parts of the period, but the difference is In 1868, the small values occur principally towards the end of Phil, Mag. S. 4, Vol. 44. No. 291, Aug. 1872. GEOLOGICAL SOCIETY. [Continued from vol. xliii. p. 544.] February 7, 1872.-Joseph Prestwich, Esq., F.R.S., President, in the Chair. The following communications were read: 1. "Further Notes on the Geology of the neighbourhood of Malaga." By M. D. M. d'Orueta. Communicated by the President. In this paper, which is a continuation of a former note laid before the Society (see Q. J. G. S. xxvii. p. 109), the author commenced by stating that his former opinion as to the Jurassic age of the rocks of Antequera is fully borne out by later researches upon their fossils. They apparently belong to the Portlandian series. The author made considerable additions to his description of the Torcal, near the foot of which he has found a sandstone containing abundance of Gryphæa virgula and Ostrea deltoidea. This he regards as equivalent to the Kimmeridge Clay. In the Torcal he has also found a soft, white, calcareous deposit, overlying the limestones of supposed Portlandian age, and containing a fossil which he identifies with the Tithonian Terebratula diphya. The author discussed the peculiar forms assumed by the rocks of the Torcal under denudation, which he supposed to be due originally to the upheaval caused by the rising of a great mass of greenstone, portions of which are visible at the surface on both sides of the range, 2. "On the River-courses of England and Wales." By Prof. A. C. Ramsay, LL.D., F.R.S., F.G.S. The author commenced by describing the changes in the physical conformation of Britain during the Jurassic and Cretaceous periods, and the relations which the deposits found during those periods bore to the Paleozoic rocks of Wales and the north-west of England. He stated that the Miocene period of Europe was essentially a continental one, and that it was closed by important disturbances of strata in Central Europe, one effect of which would be to give the Secondary formations of France and Britain a slight tilt towards the north-west. To this he ascribed the north-westerly direction of many of the rivers of France; and he surmised that at this period the rivers of the middle and south of England also took a westerly course. The westerly slope of the Cretaceous strata of England was also, he considered, the cause of the southern flow of the Severn, between the hilly land of Wales and the long slope of chalk rising towards the east. The Severn would thus establish the commencement of the escarpment of the Chalk, which has since receded far eastward. The author believed that after the Severn had cut out its valley the Cretaceous and other strata were gradually tilted eastwards, causing the easterly course of the Thames and other rivers of southern and eastern England. In these and other cases adduced by the author, the sources of these rivers were originally upon the Chalk near its escarpment; and it is by the recession of the latter |