224 Reviews — Prof. Daly — Underground VoloAile Agents. 



11. Dtnamic Mexamorphism (orogenic movement a causal 

 condition). 



1. (Tenaperature low) Dt/namo-h]/dral or slaty {?) meta- 



morphism. 



2. (Temperature high) Dynamo-thermal or friction meta- 



morphism. 

 III. Dynamo-static Metamorpiiism {load metaraorpliism in 

 rocks lying beneath overthrust masses). 

 B. Local Metamorphism (caused by eruptive bodies). 



I. Contact Metamorphism (magmatic influence in control). 

 II. Load-Contact Metamorphism (combination of load and 

 magmatic influences). 



To discuss the merits of these subdivisions would demand more 

 space than it is permissible here to take up, and tbose who are 

 interested will find a vigorous stimulation to thought in the paper 

 itself. Whether or not one agrees with all of Professor Daly's 

 proposals, one may at least congratulate him on an earnest and 

 valuable attempt to reduce a subject of extreme difficulty from 

 a state of comparative chaos to one of at least theoretical order and 

 system. 



Arthur Holmes. 



V. — Genetic Classification of Underground Volatile Agents. 

 By E. A. Daly. I:go71. Geol, xii, p. 487, 1917. 



rilHE author proposes and discusses the following classification : — 



A. Magmatic or Hypogene (includes volcanic and plutonic). 



I. Juvenile (primitive, virgin, original-magmatic), 

 («) In liquid magma. 



(h) In crystallized igneous rocks and minerals, as 

 occlusions, solid solutions, and chemical compounds. 

 ((?) Expelled, from magma or igneous rock by crystalli- 

 zation or heat ; may remain free or go into solid 

 solution or new chemical compounds. 

 II. Hesurgent (secondary-magmatic). 

 («), {h), and (c) as above. 



B. Epigene or Epigeal (includes underground atmospheric and 



marine water and associated gases). 

 I. Seepage (fresh or marine waters of infiltration). 



1. Vadose (above the water-table). 



2. Phreatic (below the water-table). 



(«) Arrested (free, occluded, in solid solution, or in 



chemical combination). 

 (b) Migrating, because of gravity, the earth's general 



heat, the heat of orogenic crushing, or the heat of 



igneous intrusion. 

 II. Connate (fresh or marine waters buried with sediments 



or surface volcanics). 

 («) Stagnant (free, occluded, in solid solution, or in 



chemical combination). 



