Dr. F. A. Bather— A Crinoidfrom the Red Crag. 205 



we may eventually crush it, but we cannot succeed in nioviug it. 

 The conclusion is quite striking, and so far we cannot but agree with 

 Mr. Keade's opinion. 



But are we entitled, therefore, to condemn the theory of the Alpine 

 overthrusts ? I think the comparison is not quite fair. First, it may 

 be remarked, the bed maj' not be horizontal but inclined ; in this case 

 the component of gravity is sufficient, at an inclination of 1 : 6'5, to 

 put the block in sliding motion, and we need not apply any external 

 pressure at all. And what seems still more important, nobody ever 

 will explain Alpine overthrusts in any other way than as a phenomenon 

 of rock-plasticity. Suppose a layer of plastic material, say pitch, 

 interposed between the block and the underlying bed ; or suppose the 

 bed to be composed of such material : then the law of viscous liquid 

 friction will come into play, instead of the friction of solids ; therefore 

 any force, however small, will succeed in moving the block. Its 

 velocity may be small if the plasticity is small, but in geology we 

 have plenty of time ; there is no hurry. 



Some features of these phenomena have been beautifully illustrated 

 by Professor Sollas' pitch-experiments. Pitch is not the same as 

 rock undoubtedlj', a point which Professor Bonney lays much stress 

 upon in the August JSumber, 1907, of the Quart. Journ. Geol. Soc, 

 but, on the other side, let us realize the difference between two months 

 (required for Professor Sollas' experiments) and hundreds of thousands 

 or millions of years which must be allowed for the analogous process 

 in the Alps. The analogy shows mountain-building to be a very slow, 

 gradual process, in virtue of the smallness of plasticity, but it would 

 be in the main a continuous process, and I do not think we are forced 

 to assume its discontinuity, as ilr. Mellaid Eeade seems inclined to do. 



The plasticity of rocks in greater depths is to be explained partly 

 by elevation of temperature, partly by pressure. But whatever ex- 

 planation we accept, there are too many evidences to deny the fact. 



In conclusion, we must say Mr. Mellard Reade's paper is very 

 instructive ; indeed, it helps us to see, by contrast with the author's 

 ideal example, what are the most essential features of the process as 

 displayed in Nature. 



III. — A Crinoid {Teteacbinus [?] felix, n.sp.) from the Red Ceag, 



By F. A. Bathek, M.A., D.Sc, F.G.S., etc. 



(PLATE VIII.) 



"R. P. G. H. BOSWELL, F.G.S., has kindly submitted to me 

 a crinoid fragment found by him on August 20, 1908, in the 

 Red Crag of Felixstowe cliffs, Suffolk. Although the specimen is 

 somewhat obscure, it is of sufficient interest to warrant a brief note. 



"The exact position of the place," writes Mr. Boswell, "was 

 half-a-mile east of Felixstowe Church (JSTewbournian Zone of Red 

 Crag). In the course of eight years' acquaintance with the Crags, 

 having sifted for three years, I have not met with any other specimen 

 of a crinoid, but Mr. F.' W. Harmer, F.G.S., teUs me'he has met with 



