Vui TABLE OF CONTENTS. 



Laurontian, and the dioiites and porphjries to the Cambrian, which he then 

 considered the equivalent of the Huronian, 416 ; he also says that the presence 

 of the Eozobn "can no longer serve to identify the Laurentian system, 416; 

 Hunt, in 1870, further discusses the geology of Eastern Massachusetts, 416, 

 417 ; comments on the views there expressed, 417, 418. C. H. Hitchcock, in 

 1871, publishes a geological description of Massachusetts, 418 ; some of his 

 errors pointed out, 418. Hunt, 1871, refers the felsites of Eastern Massachu- 

 setts to the "great Huronian system," 418. 



Hyatt, in 1871, considers the porphyries of Lynn and vicinity to be metamorphic 

 sedimentary rocks, 418, 419 ; Hunt, in 1871, takes a similar view, referring 

 these porphyries to the Huronian, and "the limestones, with Eozoon from East- 

 ern Massachusetts," to the Laurentian, 419 ; some comments on Hunt's method 

 of misrepresenting statements previously made by himself, 419, 420 ; Hunt 

 again, in 1871, holds that the gneisses and limestones of Eastern Massachusetts 

 are Laurentian, 420. Dodge's classification of the rocks near Boston, 420, 421. 

 Bouv6, in 1876, considers the felsites to be derived from the metamorphosis of 

 the conglomerates, 422 ; these views supported by Hyatt, 422, 423. Crosby, 

 in 1876, divides the " Eozoic rocks " of Massachusetts into Norian, Huronian, 

 and Mont Alban, considering these divisions "as both lithological and chrono- 

 logical," 423 ; the same statement affirmed in 1880, 423, 424 ; extraordinary 

 nature of the views here advocated, 424 ; errors in Crosby's determinations of 

 the rocks, 424. Crosby maintains that granites are derived from sedimentary 

 rocks, 424 ; liis mistakes as to the real character of the Rockport granite, 425 ; 

 he considers the felsites near Boston to be of sedimentary origin, 426, 427 ; his 

 ideas in regard to the Huronian, 427 ; in regard to the argillite and conglomerate 

 near Boston, 428. Wadsworth's investigations, in 1877, of the dikes near 

 Boston, 428 ; in 1878, of the Rockport granite, 428. Crosby, in 1879, advo- 

 cates the theory that the felsites are of deep-sea origin, or made of the red clay 

 deposited at the bottom of the ocean, 428, 429. Wadsworth studies, in 1878-79, 

 these felsites, in the field and microscopically, and makes them out to be old 

 lavas, 429 ; the felsites seen by him in the form of dikes, 429. Diller, in 1880, 

 makes an exhaustive investigation of the felsites north of Boston, and confirm.^ 

 in all respects Wadsworth's views, 430, 431 ; his field of work and collections 

 carefully examined by the authors of the present paper, and the accuracy of his 

 results testified to, 431. Crosby, in 1880, designates what he previously had 

 called i.ne "Norian " as the "Naugus Head series" ; this he considers the real 

 base of the geological column in Massachusetts, 431, 432 ; Wadsworth finds the 

 Naugus Head series to be of similar character to the zircon syenite of Norway ; 

 Crosby's views shown to be incorrect, 432, 433. Crosby's ideas in regard to 

 the Huronian in Eastern Massachusetts, 433-435 ; his views criticised, and his 

 reported facts showm to have, in many instances, no other basis than his own 

 inability to distinguish between diff'erent rocks, 436. 



Shaler, in 1879, maintains that the shales and conglomerates of Roxbury pass into 

 the amygdaloidal melaphyr, 437 ; his theoretical deductions, made in accordance 

 with this view, 437 ; Benton, in 1880, controverts these views, and shows that 

 the melaphyr is an old, altered basalt, 437. Discussion in regard to the plas- 

 ticity of the pebbles in the conglomerate, 437, 438 ; opposite views of Crosby 

 and Wadsworth, 438 ; the spindle-shape, into which Crosby thought that the 



