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THE JOURNAL OF GEOLOGY. 



present rock. Such types are called archaiomorphic. To this 

 group belong all the eruptive rocks. Through alteration, trans- 

 port, and reconsolidation new groups are formed, known as neo- 

 morphic, which are further divided according to the manner and 

 condition in which the material has been transported, and the 

 way in which the constituents have acquired their present 

 form. There are three groups of these neomorphic rocks. 

 Group 2) includes rocks whose material was in another form and in 

 another part of the earth's crust, but the form of whose con- 

 stituents has been acquired without outside influence. These 

 are the chemical precipitates and are designated as authi-lyto- 

 morphic. 

 Group 3) includes rocks which originated in another place but through 

 transportation have been brought in a solid condition to the 

 present location and united into a new rock with the old form. 

 These are the mechanical sediments, and they are called allothi- 

 stereomorphic. 

 Group 4) includes rocks composed of constituents whose material was 

 originally deposited on the place where they are now found, but 

 which have in a mechanical or chemical manner built a new 

 rock on the old place. Here are placed the products of con- 

 tact and regional metamorphism and weathering, and they are 

 designated as authi-neomorphic . 

 Each of these three neomorphic divisions under altered conditions 

 passes over into the other two, but all originate from the first division, 

 or archaiomorphic. The various possibilities are shown in the. direc- 

 tions of the arrows in the following diagram given by Dr. Milch : 



ANTHI-NEOMORPHIC 



A 



ANTHI-LYTOMOR- <r 

 PHIC 



■ALLOTHI-STEREO- 

 MORPHIC 



ARCHAIOMORPHIC 



