Reviews — A. Strahan — Geology of Purheck S^ Weymouth. 167 



Rookall occurs. The sources of information for these charts are 

 the logs of Her Majesty's ships since 1830 and of vessels in the 

 Mercantile Marine since 1854:. 



Mr. H. N. Dickson, of the Chemical Laboratory, University 

 Museum, Oxford, gives the results of a series of analyses by which 

 the degree of salinity of a number of samples of sea- water collected 

 off Rockall was determined. 



The memoir concludes with a series of Eeports on the Natural 

 History of Eockall and the surrounding seas. That on the 

 Ornithology is by Mr. J. A. Harvie Brown ; that on the Mollusca 

 by Mr. A. E. Nichols, of the Science and Art Museum, Dublin ; that 

 on the Crustacea by Mr. W. T. Caiman, B.Sc, and Professor E. P. 

 Wright; that on the Chsetopoda by Professor M'Intosh ; that on 

 the Echinodermata by Mr. W. P. Sladen ; that on the Polyzoa by 

 Miss L. R. Thornelly ; and that on the Sponges by Professor R. von 

 Lendenfeld. 



Professor T. Rupert Jones, who has been untiring in his efforts to 

 obtain new light on this most interesting locality, contributes a very 

 valuable sketch of the previous history of Rockall, and a general 

 epitome of all that has hitherto been published concerning it. 



The memoir is well illustrated by three coloured drawings of 

 Rockall from sketches by the Rev, W. S. Green ; six photographs of 

 the rock taken from different directions; a beautiful plate, showing 

 the characters of the two types of ' rockallite ' as seen in thin slices 

 under the microscope, drawn by the skilful hand of Mrs. Cole ; and 

 twelve charts showing the directions of currents around Rockall 

 during every month of the year. 



The Royal Irish Academy is to be congratulated upon their 

 spirited attempt to gain new light upon this interesting locality, and 

 no less so on the manner in which the results achieved have been 

 presented to the public in their ' Transactions.' 



K, :B "V" I IB 'VT s. 



I. — Memoirs of the Geological Survey of England and 

 Wales. "The Geology of the Isle of Purbeck and Wey- 

 mouth." By Aubrey Strahan, M.A., F.G.S. 8vo : pp. xi and 

 278; 5 plates from photographs, 2 folding plates, and 183 other 

 illustrations in the text ; map and 3 plates of sections at the end 

 of the book. (London, 1898. Price 10s. Qd.) 



IN his preface the Director-General of the Geological Survey 

 remarks that "when the revision of the Geological Survey maps 

 of the Isle of Wight was completed in 1888, it was deemed advisable 

 to continue the work into the adjacent parts of Dorset. The task 

 of resurveying the classic Isle of Purbeck and the region round 

 Weymouth was entrusted to Mr. A. Strahan, who had mapped the 

 Secondary formations of the Isle of Wight. In two years the 

 field-work was finished as far as the top of the Chalk, and the 

 mapping of the Tertiary deposits was subsequently completed by 

 Mr. 0. Reid." 



