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1875 and 1878. He wrote for the Second Geological Survey 

 of Pennsylvania a special report on the " Trap Dykes and 

 Azoic Eocks of Southeastern Pennsylvania." He completed 

 only the first part, a volume of 253 pages, consisting in the 

 main of the historical introduction. The director, Dr. J. P. 

 Lesley, in his letter to the commissioners of the Survey, after 

 explaining the work done by three of the geologists of the 

 regular corps, adds : "In support of the assiduous studies of 

 those gentlemen of the azoic rocks in their respective dis- 

 tricts, and to further the success upon which they can already 

 congratulate themselves, it was unquestionably desirable to 

 compare their observations and conclusions with those made 

 and reached by geologists outside of the State, in the azoic 

 regions of New Jersey, New York, New England, and espe- 

 cially Canada. No better plan could have been adopted to 

 reach this end than to invite so distinguished a student of 

 azoic geology as Dr. Hunt to visit those districts of our sur- 

 vey which seemed to correspond with those in the North, 

 among which he has spent the best part of his laborious and 

 successful life, and no book could be more useful than one in 

 which he should collate all the known, supposed and sus- 

 pected facts of American azoic geology, with all the accepted 

 conclusions, and proposed hypotheses, published on the 

 subject by the most eminent geologists of the last half cen- 

 tury in Europe and America. 



u We owe, therefore, a debt of gratitude to Dr. Hunt for 

 this historical monograph which will supply a deeply felt 

 deficiency in the literature of our science. It is a treasury 

 of notes and suggestions, of the greatest value to the geolo- 

 gists of Pennsylvania and of other States, working in such 

 districts as are occupied at the surface or are underlaid at 

 moderate depths by the Cambrian ar.d sub -Cambrian forma- 

 tions, although no final demonstration has been accomplished 

 by the author of these problems of superposition, unconfor- 

 mability and identification at which so many geologists are 

 still half despairingly at work. But his opinion of the 

 probable final solutions of these problems will reinforce their 



