ADDENDA. 



Page 65. In the report of the State Geologist of Michigan for 

 1891-92 (issued January, 1893), pp. 144, 145, Dr. M. E. Wadsworth 

 has published a " Preliminary Classification of Metalliferous or 

 Ore Deposits." The main outline is as follows : 



I. Eruptive Deposits (a) Non-Fragmental. 



(b) Fragmental. 

 II. Mechanical Deposits (a) Unconsolidated. 



(b) Consolidated. 

 III. Chemical Deposits (a) Sublimations. 



(b) Water Deposits. 



(c) Impregnations or Replacements. 



(d) Segregations or Cavity Deposits. 



Each of the above except III. (d) is then subdivided so that 

 the table becomes practically a classification of rocks. Indeed, a 

 moment's consideration will show that the scheme in its main divis- 

 ions is closely modeled after the prevailing classification of rocks. 

 III. (d) Segregations or Cavity Deposits contains the following : 

 1. Pockets. 2. Chambers. 3. Contact Deposits. 4. Veins, in- 

 cluding Gash Veins, Segregated Veins, Reticulated Veins or Stock- 

 work, Contact Veins, Fissure or Fault Veins. 



The author states in some appended comments that the table 

 is not limited to those deposits now practically worked (which we 

 ordinarily understand the expression ore deposits to mean), but is 

 intended to include all that have been or may be of value. But in 

 this respect there is good ground for preferring to make our clas- 

 sifications in ore deposits, as in mineralogy, zoology, etc., embrace 

 only the authenticated varieties, expecting additions to be incor- 

 porated as discovered and suitably described. 



Page 73. In connection with the precipitation of iron ores by 

 limestones, an added note on the chemistry of the reaction is.desira- 

 ble. Dr. J. P. Kimball, in a paper on the " Genesis of Iron Ores 

 by Isomorphous and Pseudomorphous Replacement of Limestone," 



