312 Reviews — C. D. Walcott's Cambrian Bracliiopoda. 



The important discoveries of Silurian (Ludlow) fossils made by 

 Mr. Green and Mr. Sherborn in " Black slates "with limestone 

 lenticles " at Fletching's Cove near Porthalla (Portliallow on map), 

 and in the "Slates with inclusions" at Nare Cove, south of J^are 

 Head, do not prove tliat the inclusions and lenticles are of a con- 

 glomeratic character and of Devonian age. In such a region of 

 faulting and thrusting and probable infolding, it would seem more 

 likely that the inclusions have been brought about by disturbance. 

 The fact observed by Mr. Hill that the Manaccan conglomerate 

 contains fragments of the Portscatho rocks, etc., does not appear to 

 have been taken into consideration by Mr. Green and Mr. Sherborn, 

 and this evidence strongly favours Mr. Hill's view that the Manaccan 

 conglomerate forms the local base of the Devonian. It is to be 

 hoped that these three geologists may be able in due course to 

 harmonize their views. Materials for the definite determination of 

 some of the problems are still wanting. It has been pointed out 

 that the absence of any fragments of the Lizard Series in the Ordovician 

 and Devonian rocks of the area is remarkable, and cannot he satis- 

 factorily explained ; and there are features that have led Mr. Hill to 

 see evidence of a transitional passage from the Very an group into 

 tlie Lizard Series. The facts for and against this hypothesis are fully 

 discussed in the memoir, wherein it is stated "that this difficult 

 problem is not yet by any means settled".' 



In thus referring to the chief controverted subjects, we have no 

 space in which to enlarge on the accessions to knowledge in reference 

 to the various igneous rocks and to metamorphism. It should be 

 mentioned, however, that apart from the Lizard Series there are 

 pillow-lavas (spilites), granite, elvans, and mica-traps in the northern 

 area, and these are duly described. Some account is given of the 

 possible derivation of the Gunwalloe beach-shingle from an old 

 Eocene deposit, and then follow descriptions of the Pliocene gravels, 

 raised beaches and head, submerged forests, and coast erosion. 

 An interesting and instructive account is given of the soils and 

 agriculture, followed by notes on the water supply, building materials, 

 serpentine industry, and mining, to which last subject Mr. D. A. 

 MacAlister has contributed. 



The plates include excellent views of scenery, rock-structures, and 

 photomicrographs of rocks, and among them is one of a " Glacial 

 Boulder on the Beach at Porthleven ". This, known as the " Giant's 

 Rock ", is a block, about 50 tons in weight, of " microcline gneiss of 

 a type unknown in Britain ", and has evidently been derived from 

 the raised beach. 



II. — Primitive Bkachiopods. 

 Cambrian Brachiopoda. By Charles D. Walcott. Monographs of 

 the United States Geological Survey, vol. li, part i, pp. 1-872 ; 

 part ii, pp. 1-363; plates i-civ. 4to. "Washington, 1912. 



THIS immense work is another example of the wondei'f ul energy 

 of American scientific investigators, and is a further proof of their 

 very comprehensive grasp of their subjects. Not alone the students 



' See also Hill, Proc. Geol. Assoc, xxiv, p. 153, 1913. 



