138 ■ Correspondence — Mr. John Young. 



The evidence now adduced - proves (1) that the 'Fucoid Beds' 

 and ' Serpulite Grit ' are of Lower Cambrian age, the underlying 

 quartzites forming the sandy base of the system ; (2) that the 

 Torridon Sandstone, which is everywhere separated from the over- 

 lying quartzites by a marked unconformability, is pre-Cambrian. 



The Olenellus which has been discovered is described as a new 

 species (0. Lapicorthi) closely allied to 0. Thompsoui, Hall, from 

 which it differs chiefly in the arrangement of the glabella-furrows- 

 and in the presence of a rudimentary mesial spine at the posterior 

 margin of the carapace. Remains of other species referable to 

 Olenellus are described, but these are too fragmentary for exact 

 determination. All are chai'acterized by a reticulate ornamentation 

 similar to that described by Walcott in 0. (Mesonacis) asaphoides, 

 Emmons. The remains consist chiefly- of portions of carapaces. 



COiKIRESI^OIsriDEIiTGE. 



CONE-IN-CONE STEIJCTURE. 



Sir, — In the present February No. of the Geological Magazine, 

 Mr. A. C. G. Cameron in his paper on the " Kellaways Beds " makes 

 reference to an indurated seam of sandy marl that exhibits Cone-in- 

 cone Structure, and refers to an abstract in Geol. Mag. of a paper 

 of mine, that is printed in Trans. Geol. Soc. of Glasgow, in which 

 I give an explanation of the above-mentioned structure. In this 

 paper I am credited by Mr. Cameron with stating that in cone-in- 

 cone structure, the apices of the cones point towards each other iu 

 the beds in which this structure is found. Had Mr. Cameron read 

 the full text of my paper, he there would have seen that this state- 

 ment was not mine, but was given in two of the quotations, illustrat- 

 ing some of the views formerly held by those that had written on 

 cone-in-cone structure. Thus, H. C. Sorby, F.E.S., is quoted as 

 having written — "The cones often occur in bands parallel to the 

 stratification of the rock, their apices starting from a well-defined 

 plane, and after extending upwards or downwards for a greater or 

 less distance with their axis perpendicular to the plane of stratifica- 

 tion, they end in bases parallel to it but not on the same level, some 

 standing up above the general surface." The other quotation is 

 from the Students' Manual of Geology, by Prof. J. B. Jukes, edited 

 by Prof. A. Geikie, 1872. It is there stated that " some clay iron- 

 stones exhibit another concretionary form called * cone-in-cone,' as 

 the seam of ironstone breaks into conical forms, with the bases of 

 the cones at the top and bottom of the seam, and their apices pointing 

 inwards towards each other." 



In my paper I have written against this statement, in both 

 quotations, of the cones ever having their apices pointing inwards 

 towards each other, and state, "lam inclined to think that such 

 a description is due to faulty observation, or could only have been 

 made from a badly preserved specimen, in which the structure was 



