1 846 LETTER FROM L YELL 87 



you represent. But as I interpret your paper, you think the period 

 so short that you have only time for one gigantic effort to cause 

 all the faults, fissures, and curvatures of the older strata. You may 

 say, perhaps, that the greater time taken for the denudation the 

 less remains for the upheaval; but that argument is then against 

 the two operations having been contemporaneous. That you do 

 not suppose them to have gone on simultaneously I conclude from 

 the suddenness which you attribute to the action of the disturbing 

 forces. You also seem to assume (p. 317) that the action of forces 

 working at successive times could be conflicting. This seems to be 

 so contrary to the analogy of volcanic action, whether breaking out 

 at the surface or exhibited in the upheaval or depression of con- 

 tinents, or in convulsions which rend for several thousand years 

 lines of country, recurring so marvellously in the same tracts, and 

 in the same direction, that some facts or some references to con- 

 trary analogies should have been given. The conformity of the 

 Palaeozoic strata can in no wise circumscribe the lapse of time of 

 which I have defined the limits as above. 



I do not think that any geologist who has lived, as we have 

 done, in a period when a single earthquake can rend a large district 

 like Chili, and permanently uplift a portion of the earth's crust, 

 which may possibly be miles in depth, will quarrel with you for any 

 intensity which you ascribe to the disturbing power ; but I shall be 

 surprised if you do not live to see the day when few will think it 

 consistent either with the ancient Plutonic or Trappean phenomena, 

 or with our acquaintance with actual igneous action, to suppose that 

 so mighty a change in the interior of the earth occurred at once, as is 

 implied by the sudden uplifting and contortion of thousands of feet 

 of strata. That no relief should have been obtained by intermittent 

 action, as now by the rending of the crust as soon as the expansive 

 power of the melted matter requires more room, but that it should 

 have all been kept under till it could be accommodated during one grand 

 convulsion is, I suspect, an hypothesis unnecessary on mechanical 

 grounds, and especially undesirable by one who adopts our views of 

 denudation, which are so naturally aided by taking not only un- 

 limited time for the development of igneous action, but equally so 

 as regards the upward and downward movements, and the rending 

 and bending of the beds. But I do not write this to make a con- 

 vert of you, but that you may explain if I have misconstrued your 

 meaning, and you will better see how I interpret you by my entering 

 into this line of objection. I do not quite follow you on the argu- 

 ment founded on the missing members ; but I am sure you cannot 

 assume that, in a region suffering denudation, deposits of such a 

 nature as to last must be found in the immediate neighbourhood. 

 It is, I believe, quite the exception to the rule, and in this view I 

 am not singular. Hoping to hear from you soon, and with many 



