Correspondence — Mr. A. J. Jukes-Browne — Dr. G. Solm. 139 



obscure or mucli confused." I also further state, " that the apices 

 are invariably turned to the under or lower side of the stratum, 

 while their bases are as invariably directed to the upper surface." 



In my explanation of cone-in-cone structure, I point out that it 

 was probably due to a mechanical action, set up through chemical 

 agencies, such as gases, that were generated by the decomposition 

 of the organic matter present in the lower portion of the stratum, 

 the elevatory power of such gases, as they escaped upwards to the 

 surface of the bed, through the tube forming the central axis of each 

 cone, brought up from below the successive layers of plastic mud, 

 of which the cone structure is seen to be built up. 



HuNTERiAN Museum, University Glasgow, John lOUNG. 



February Uth, 1892. 



EEADE'S THEORY OF MOUNTAIN BUILDING. 



SiK, — In reply to Mr. Eeade I am quite aware that he replied 

 to Mr. Davison's argument last year, but in the opinion of good 

 physicists that reply was no answer. Mr. Keade apparently failed 

 to realize Mr. Davison's meaning, and the further explanation given 

 in the postscript to my paper does not seem to have made it clearer 

 to him. 



My own ideas of the result of subsidence do not form the primary 

 question in debate, which is — can we accept Mr. Eeade's ideas? 

 It is eminently desirable, therefore, that he should address himself 

 to Mr. Davison's objection and postpone any consideration of my 

 criticisms. 



I am obliged to Mr. Eeade for pointing out the error in my figures ;. 

 an has been omitted, but when supplied makes the case against 

 him ten times worse than before. If I have misunderstood Mr. 

 Eeade's idea of expansive compression, or if my argument is un- 

 sound, I shall be glad to be corrected. A. J. Jukes-Bkowne. 



Exeter, Feb. 10. 



CONCERNING THE DIMENSIONS OF OLENELLUS. 



SiK, — In his excellent paper " On OleneUus Callavei," in the 

 Geol. Mag., Dec, 1891, p. 529, Professor C. Lapworth says: "The 

 larger fragments collected indicate a length of about six inches and 

 a breadth of about four inches. With the exception of OleneUus 

 (Hohnia) Broggeri, Walcott, this form is the largest species of the 

 genus yet discovered." Prof. Lapworth seems to have overlooked 

 that OleneUus (Holmia) Kjerulji, Linns., might reach fully the length 

 of 0. {H.)Callavei. In my paper "On OleneUus Kjerulji," in Geolog. 

 foren. forhandl. vol. ix. (1887) p. 512, I have stated that: "The 

 largest specimen I have found has a breadth of 63 mm. between the 

 eyes." The length of the body must, therefore, in this case, have 

 been 155 mm., which is more than six inches. 



Gerhakd Holm. 



