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THE POPULAR SCIENCE MONTHLY. 



New Hampshire. 1 The rocks have been carefully studied stratigraphi- 

 cally and lithologically, so that their place in the column is well under- 

 stood, and the fossil is so allied to the Eozoon as to abundantly con- 

 firm all that has been held for it by its warmest advocates. 



As a matter of convenience Mr. Hawes proposes to call the group 

 of rocks affording these organisms greenstones, in allusion to their 

 color. They have not been melted like a certain class of traps once 

 called by this name, but have been metamorphosed somewhat; they 

 embrace most of the chloritic and talcose schists, or, technically, " all 

 basic metamorphic rocks whose predominant coloring ingredient is 

 either hornblende, pyroxene, or chlorite." Those of special interest to 

 us now are varieties of diorite and diabase, the first consisting mainly 

 of hornblende and feldspar, the second adding labradorite to the con- 

 stituents of the first-named rock. These rocks by many authors are 

 regarded as of igneous origin. 



Fig. 7. Protozoan Fossil, proeablt Stromatopora, from Connecticut Lake, N. II. 



The method of examination employed in determining the composi- 

 tion of these greenstones is of some interest. A bit of the specimen 

 is carefully ground to the thinnest dimensions possible, so that it can 

 be examined optically under the microscope. With common and 

 polarized light it is possible to understand the nature of the minutest 

 minerals present, as well as the cavities contained in them. The study 

 of rocks in this way has been prosecuted so energetically of late, that 

 it is common to speak of the sub-sciences micro-lithology, micro- 

 petrology, etc., and the appearances ol every mineral are now well 

 understood by those skilled in observation, so that the conclusions are 

 often more reliable than those obtained by ultimate chemical analysis. 

 Mr. Hawes combines in his studies the use of the microscope and chem- 



1 American Journal of Science, iii., vol. sii., p. 134. 



