Geology. 301 



called the writer's attention to an error in the calculation of the 

 norm of " neponsetose," * namely, the calculation of hypersthene 

 with nephelite. Since the former of these constituents by taking 

 up silica increases the amount of nephelite, this error led to plac- 

 ing the rock in the wrong order (II. 6.2.5.). The publication of 

 the correction has been delayed in order to secure a new and com- 

 plete analysis of the freshest material obtainable of the andesitic 

 lava. 



Specimens from five localities, most kindly collected for the 

 writer by Prof. W. O. Crosby, were sectioned and field observa- 

 tions, macroscopic, and microscopic study were utilized in select- 

 ing the material from which the following analysis has been made 

 and the following norm calculated. The rock falls in Class II, 

 order 5 (6), rang (1) 2, sub-rang "5. 



Analysis of Neponsetose. f 



Norm 



Orthoclase 6-67 



Albite 4768 



Anorthite 6*12 



Nephelite 8-52 



Diopside 7*34 



Olivine 6*80 



Magnetite 7*42 



Ilmenite 3*19 



SiO, . - . 



50-09 



A1.0,- 



15-84 



Fe 2 3 - 



7-44 



FeO... 



3-80 



MgO .. 



4-98 



CaO... 



3-54 



Na 2 . . 



7-50 



K 2 0... 



1-10 



H,0± 



3-67 



CO,... 



0-34 



TiO a . 



1-70 



P.O.— 



0-32 



MnO 



trace 





100-32 





II. 5(6). (1)2 



Hematite 2-40 



Apatite ' -67 



H 2 0± 3-67 



CO... -34 



100-30 



4. Cambrian Trilobites ; by Charles D. Walcott. Smith- 

 son. Misc. Coll., vol. 64, No. 3, 1916, pp. 157-259, pis. 24-38.— 

 Here are described 68 forms of trilobites, of which 49 are new, 

 the new genera being Menomonia [M. calymenoides has 42 

 thoracic segments), Millardia, Dresbachia, Norwoodia, Saratogia, 

 Vanuxemella, and Hanburia. The first four of the above genera 

 are of the order Proparia. The genus Crepicephalus now has 17 

 species. Besides the paleontological value of the paper, more 

 stratigraphic evidence is now at hand for the correlation of 

 Middle and Upper Cambrian formations in North America. The 

 Weeks formation of the Cordilleran region is transferred from 

 the Middle to the Upper Cambrian and the Conasauga formation 

 of Alabama, while in the main Upper Cambrian, also seems to 

 have Middle Cambrian trilobites. c, s. 



*Op. cit., p. 153. 



f Specimen from Delhi Street, Mattapan, Suffolk County, Mass. Wm. T. 

 Hall, Analyst, Laboratory of Analytical Chemistry, Boston, Mass. 



