1847.] Correspondence. 105 



There are many men who take all opportunities to proclaim their 

 excellence. They really have no faith themselves in their own 

 works, and hence feel that the faith of others must be quite feeble 

 unless they greatly magnify their own doings. 



CORRESPONDENCE. 



The following extract from a letter which we have just received 

 from the Rev. Prof. Sedgewick, of Cambridge, we consider suf- 

 ficiently interesting, at least to a part of our readers, for insertion 

 in the Journal. It relates, it is true, to the geology of a distant 

 country, but still contains important facts which bear upon 

 American geology. After expressing in a general way a strong 

 desire to visit this country, Prof. Sedgewick introduces his subject 

 by remarking, that " In one important respect I am certain that I 

 agree with you. We have an enormous thickness of fossilifer- 

 ous slates, &c., below any rocks to which the name Silurian sys- 

 tem can be given with any geographical propriety; for they exist 

 in Cambria, but are not found in Siluria. 



The change introduced by Sir R. I. Murchison about three 

 years since, without my concurrence, w^as this; he sponged out 

 his base line and removed it to the west side of Wales, and then 

 he split his Silurian system into two systems — making his lower 

 system to comprehend the so called Cambrian rocks. This change 

 not merely introduced a geographical inaccuracy of correlation, 

 but went on a mistaken hypothesis, viz: that the fossil band in north 

 Wales was the equivalent of the Caradoc sandstone and Llandielo 

 flag stone repeated again and again, by undulations. I have 

 sifted this to the bottom and am certain that the hypothesis is not 

 true to nature. 



My scheme of arrangement for the lower stratified rocks of this 

 Island, (and let each country be worked out on its own evidence, 

 before we begin to institute close comparisons) is as follows: 



Class 1. Hypogene. 



Class 2. PaljEozoic. 



{1. Cambrian. 

 2. Silurian. 

 3. Devonian. 

 4. Carboniferous. 

 Between each of those four systems I interpolate an intermediate, 

 or transition group. Thus the Cambrian system ends in the ascend- 

 ing order w^th a Cambro-silurian group. 



Speaking again of the Cambrian system, Prof. Sedgewick re- 

 marks that it is of enoimous thickness, perhaps not less than 



