wAKii.j NATURE AXD EXTENT OF THE LARAMIE GROUP. 435 



the case, and also afifords a rude index to tlie rate of deposition, since 

 only such objects could be preserved as succeeded in being covered up. 

 Thus by ascertaining the average rate of decay of vegetable substances 

 and noting the objects of maximum thickness which are found pre- 

 served, the time necessary to form a deposit of that thickness becomes 

 approximately known. 



The discussions with regard to the age of the Laramie group which 

 have been rapidly passed in review have, perhaps, sufiQciently shown 

 that it is in)i)os.sil)le to refer that group either to the Cretaceous or to 

 the Tertiary and in so doing harmonize all the facts that the group 

 presents with those in conformity with which other deposits in other ■ 

 countries of the woi Id have been so referred ; but they have also sufiQci- 

 ently shown that tbis is not the fault of the investigators, but, so to 

 speak, of the facts, and that the real disagreement is in the organic » f 

 forms and the nature of the deposits, so that omniscience itself could ' ''^*^ 

 never harmonize them with all kinds of forms and deposits in all parts 

 of the world. It is, therefore, futile, and indeed puerile, longer to dis- 

 cuss this question, and we can well afford to dismiss it altogether and 

 settle down to the more serious study of the real problems which still 

 lie before us. 



One of these problems is often confounded with the question of age, 

 which should be rigidly distinguished from it. This is the question of 

 synchronism. If it could be satisfactorily proved that the Laramie 

 group was deposited at the same absolute time as the iron sands of 

 Aix la-Chapelle, the Credneria beds of Blankenburg, or the travertines 

 of Sezanne, this would indeed be a great gain to science. But as the 

 animal and vegetable remains cannot be made to agree, it seems hope- 

 less to attempt to arrive at complete harmony in this respect. The 

 most that can be profitably undertaken is to find two or more deposits 

 widely separated geographically in which either the floras, the inverte- 

 brate faunas, or the vertebrate faunas substantially agree. With regard 

 to the invertebrate fiiunas this seems hopeless so far as the Laramie 

 group is concerned. If that group was deposited in the manner above 

 described, it would be ditiBcult to find another which owed its existence 

 to identical conditions; and if tbis state of things has occurred at more 

 than one point upon the globe, the chances are again greatly dimin- 

 ished for it to have occurred at the same period of geologic time. But 

 even supposing such a combination of coincidences possible, if the 

 Laramie forms are the modified descendants of antecedent marine 

 forms, there is no probability that the conditions at any otber point on 

 the earth's surface could be so nearly identical with those obtaniing 

 there that precisely the same modifications would take place to adapt 

 the marine forms to the brackish-water habitat. The chances are 

 therefore infinity to one against the existence of other beds that shall 

 contain an invertebrate fauna identical with that of the Laramie group.. 





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