Correspondence — Mr. Artlitir Yaughan. 93 



and the Geological Survey of the range has been executed by my 

 colleague Mr. H. H. Howell." 



From this it will be seen that the age of these rocks was 

 determined by no less an authoi'ity than Professor Sedgwick, the 

 founder of the Cambrian system in Wales, supported by his friend 

 and pupil Professor Jukes, and the ground of this determination is 

 the resemblance of the Forest beds to the Cambrian beds of North 

 Wales. Who amongst men should have been better able to recognize 

 this resemblance than the distinguished founder of the Cambrian 

 system ? Nor was the opinion of Professor Jukes less entitled to 

 weight, as Jukes spent several years of his Survey life amongst the 

 old rocks of North Wales. For six months of my own Survey life 

 I was his companion and pupil in the same region ; and when a few 

 years afterwards I had opportunities of examining the rocks of 

 Charnwood Forest I was able to recognize the similarity of physical 

 character, upon which Sedgwick and Jukes to a great degree relied 

 in determining the geological age of the rocks ; nor, notwithstanding 

 what has been written by more recent authors, am I able to see 

 good reason to alter the opinion I then held. 



Oa reading over again the brief description of these rocks (as far 

 as regards their non-plutonic masses), written at a time when their 

 characters were vividly impressed on my mind, and when there was 

 no dispute regarding their age, I see how similar is the description 

 to one which might be applied to the Lower Cambrian beds of 

 Merionethshire. " Crossing the axis we find the beds as far as 

 Upper Black Brook, consisting of bluish-purple and green slates, 

 of a coarse character, alternating with fine grits." The eruptive 

 masses are then described, and their resemblance to the contem- 

 poraneous and intrusive masses of North Wales is pointed out 

 (p. 12). Since these words were written much new light has been 

 thrown on the composition and structure of the igneous masses by 

 Professor Bonney and other petrologists. In 1860, the application 

 of the microscope to thin sections of rock was scarcely begun ; but 

 the determination of the geological age of the whole series of the 

 Charnwood rocks is not affected by microscopic definitions of the 

 eruptive beds. 



1 have still much hope that fossils may yet be discovered in 

 these old rocks. After the discovery of a Trilobite in the slates 

 of Llanberis no one need despair ; and any young geologist who 

 desires to break fresh ground and win his spurs would do well to 

 turn his attention to the slates of Charnwood Forest. 



Edward Hull. 



THE MAKING OF MOUNTAINS— A EEPLT TO MR. MELLARD READE. 



Sir, — May I ask you to allow me space to answer, as briefly as 

 possible, a letter, in the Geological Magazine for December, 1894, 

 in which Mr. Reade attacks my theory on the making of mountains. 



I must in the first place object to a statement implying that 

 I have, to a certain extent, changed front. Mr. Eeade remarks ; 

 " Mr. Yaughan now says, that he does not rely upon decrease of 



