May 8, 1879] 



NATURE 



27 



The Silurian district of Girvan in Ayrshire is one that 

 has attracted much attention from geologists, and con- 

 siderable difference of opinion has existed as to the exact 

 correlation of the several members of the formation as 

 ' there exhibited with the equivalent English deposits. The 

 fossils, though numerous, are often in a rather unsatis- 

 factory condition as regards preservation, and it was 

 most desirable that a careful study of all the known forms 

 should be made by competent palaeontologists. The 

 i richly stocked cabinets of Mrs. Robert Gray have furnished 

 ' the larger part of the specimens described, and the com- 

 pletion of this first part of the work was rendered possible 

 by the liberality of Mr. Gray. 



The memoir commences with an account of the biblio- 

 graphy of the subject, which appears to be very full and 

 complete, and then proceeds to the description of the 

 lower forms of life. Any one who will take the trouble 

 to compare the lists given by our authors with those 

 previously published cannot but be struck by the large 

 additions which are now made to the Girvan Silurian 

 f.iuna. A single doubtful fucoid and four species of 

 Foraminifera are described as occurring in the Girvan 

 rocks, and among the latter is the remarkable Saccam- 

 rnina carteri, which is so excessively abundant in some 

 of the Carboniferous limestones. This form has been 

 recognised as identical with the Carboniferous type by 

 Mr. H. B. Brady himself, and its existence in Silurian 

 strata adds another example — one of great interest to 

 geologists — of the wide range in time of some of the lower 

 forms of life. 



Among the corals from the Girvan area Messrs. 

 Nicholson and Etheridge enumerate no less^than twenty- 

 two forms, some being old and well-known species, but the 

 majority are new to science ; indeed several new genera 

 of Actinozoa are established in the present work. The 

 specimens are usually in a bad state of preservation, a 

 difficuhy which has been to some extent overcome by the 

 authors by the employment of thin sections. The fact 

 which comes out most strikingly from the study of the 

 Ccelenterate fauna of the Girvan beds is that the nearest 

 analogues of the Silurian fossils of Scotland are to be 

 found not in the English area but in the American. The 

 same fact, it will be remembered, was made very strikingly 

 manifest from Mr. Salter' s studies of the fauna of the 

 Silurian limestone of Durness in Sutherland. 



Of Trilobites twenty-eight species are now described as 

 occurring in the Girvan district, and among them several 

 forms new to science have been detected. 



As the present volume only contains the first part of 

 the results of our author' s labours we do not find a full 

 discussion of the bearing of the palseontological evidence 

 on the interesting question of the age of the several 

 Girvan deposits. There can be no doubt, however, that 

 lioth the Upper and Lower Silurian are there represented, 

 though the exact correlation of the different members of 

 the series can only be successfully attempted when the 

 fossils have been more fully worked out. 



The present fasciculus is illustrated by nine very well 



c xecuted lithographic plates from the pencil of Mr. Charles 



;rjean. We congratulate the authors on the able manner 



which they have executed this first portion of their 



lask, and hope soon to have to record the appearance of 



other portions of this important monograph. 



OUR BOOK SHELF 



Natural History Rambles. The Sea-Shore. By Prof. 

 P. M. Duncan, F.R.S. Lane and Field. By the Rev. 

 J. G. Wood. Underground. By J. E. Taylor, F.L.S. 

 The Woodlands. By M. C. Cooke, LL.D. (London : 

 S.P.C.K., 1879). 



These four handy little volumes are well put together, 

 and seem to us decidedly superior to works of a similar 

 kind with which we used to be familiar in our youth. The 

 evident purpose of the volumes is not to teach their subjects 

 systematically, but to lead those into whose hands they may 

 fall to take an interest in the common objects of nature 

 which may be met with in an occasional walk. For this 

 purpose they seem to us well adapted, and the informa- 

 tion they convey on the whole trustworthy. They abound 

 in suitable and well-executed illustrations, and might 

 appropriately be put into the hands of any one, old and 

 young, whose circumstances would give him a chance of 

 using them. 



LETTERS TO THE EDITOR 



[ The Editor does not hold himself responsible for opinions expressed 

 by his correspondents. Neither can he undertake t» return, or 

 to correspond with the writers of, rejected manuscripts. No 

 notice is taken of anonymous communications. 



[ The Editor urgently requests ctrrespondents to keep their letters as 

 short as possible. The pressure on his space is so great that it 

 is impossible othenvise to ensure the appearance even tf com - 

 munications containing interesting and novel facts. 1 



Brorsen's Comet 



Last night, May 3, I observed Brorsen's comet pa-is nearly 

 centrally over the star DM, 4- 61°, No. 873. In the principal 

 focus of the telescope were two straight bars, 43" (seconds of 

 arc) wide intersecting in the centre of the field. The bars are 

 at right angles to one another, and were inclined 45° to the hour 

 circle. With this arrangement it was easy, by moTJng the 

 telescope gently about the polar axis (which is well adjusted), to 

 determine the conjunctions in R.A. and in declination, while 

 angles of position coinciding with the bars, and distances in 

 parts of the breadth of a bar, could be estimated with consider- 

 able accuracy. In this manner I made the following observa- 

 tions of the position of the comet with reference to the star : — 



Chronometer Angle of p- , 



time. position, 



b. m. s. o /, 



-i:~ -- i Distance measured by beats of 



10 259 ... 260 ... 33] chronometer. 



10 4 31 ... 270 ... 12 Ditto. 



10 620 ... — ... — Star apparently central in comet. 



ID 730 .'.. 320 ... 10 Star a little right of centre. 



10 II 30 ... o ... — Estimated conjunction in R.A. 



10 16 o ... 45 ... 16 



10 18 15 ... 45 ... 43 



10 20 30 ... 45 ... 65 



Projecting these observations on a chart of ruled squares, it 

 appears that at loh. iim. 36s. (corresponding to loh. iim. 14s. 

 G.M.T.) the comet followed the star o'68s. in R.A. and was 

 12" N. of it, while the nearest approach of the centre of the 

 comet to the star was 7" at about loh. 7m. 



The moon was shining with great brilliancy (being nearly full) 

 and made the comet faint, reducing its apparent diameter to i J 

 or 2 minutes. The star is given in the DM as of the 8'8 mag- 

 nitude, but I think is underrated a little. While the comet was 

 passing over it there was no sensible diminution of its lustre. 

 The DM position of the star for 1855-0 is — 



a = 6h. 7m. 25s., J = -I- 61° 28'-9. 



The light of the comet has diminished rapidly since April 4. 

 It is now less bright than a 9th mag. star. 



Blackheath G. L. Tupman 



It is to be hoped that while the comet remains with us the 

 observations of Prof. Young (Nature, vol. xix. p. 559), and of 

 Mr. Chrijtie (NATURE, vol. xx. p. 5) may be repeated and con- 

 firmed by those who possess telescopes of sufficient power. 



