282 Reviews— The Dunstones of Ply mouth. 



directing attention to astronomical and dynamical memoirs which 

 they may easily overlook. The fewness of references is part of the 

 method of the book. Its attractiveness is largely due to the personal 

 element in it, which shows the mental processes by which the author 

 felt his way from the problems of glacial climates to his illuminating 

 contributions to the pre-geological history of the earth. y tv p 



II. — The Dunstones of Plymouth and the Compton-Efford Grit. 

 By It. H. Worth, M. Inst. C.E., F.G.S. Transactions of the 

 Devonshire Association for the Advancement of Science, Litera- 

 ture, and Art, xlviii, pp. 217-59, 1916. 

 IIS" this paper the author sets forth some very revolutionary views 

 regarding the Devonian igneous rocks of the Plymouth district. 

 These rocks ("the Dunstones") are described by Mr. Ussher and 

 Dr. Elett in the Geological Survey memoir of the Plymouth and 

 Liskeard district as pillow lavas (spilites), diabases, and schalstein 

 tuffs. The present author, however, comes to the conclusion that 

 the rocks which he classes together under the old name of dunstones 

 are all intrusive, there being no extrusive lava in the series which he 

 lias examined. The pillow structure which they exhibit is attributed 

 to the rolling of parts of the walls of the fissure into the dunstone as 

 it was intruded, since the pillows are generally attached to the main 

 mass of the dyke and are surrounded by a skin of baked slate. The 

 associated cherts, previously described as radiolarian cherts, are 

 regarded as silicified slates, as they only extend over a space of the 

 same extent as the dykes and are often included in the dyke or inter- 

 bedded with thin layers of dunstone. There are three kinds of 

 metamorphism associated with the intrusion of the dunstones, 

 silicification, chloritization, and dolomitization, which with the 

 baking, affect the surrounding slates, either together or separately 

 in different places. The schalstein tuffs and breccias of the Survey 

 memoir are described as being composite rocks of slate and dunstone, 

 produced by the brecciation of the sides of the fissure, accompanied by 

 the mixture of the slate fragments with the igneous rock. The 

 dunstones are therefore regarded as having been intruded into the 

 slates after they had developed a slaty cleavage. The Compton, 

 Crabtree, and Wearde grits, which have been described as volcanic 

 grits contemporaneous with the pillow lavas, are regarded as ordinary 

 sediments, produced by the weathering of pre-existing igneous rocks, 

 the evidence being drawn both from the mineral characters of the 

 grits themselves and from the variety of the pebbles in the pebble 

 bed associated with the grit and dunstone at Crabtree. 



W. H. WlLCOCKSON. 



III. — A Synopsis of American early Tertiary Cheilostome 

 Bryozoa. By Ferdinand Cantj and Bay S. Bassler. United 

 States Museum Bulletin 96. pp. 88, 6 pis. Smithsonian Institu- 

 tion. Washington, 1917. 



AS one of the authors explains in his preface, the volume is 

 a foretaste of a larger monograph on Tertiary Polyzoa ; and, 

 certainly, this hors d'ceuvre whets the appetite for what is coming. 



