402 THE AZOIC SYSTEM AND ITS SUBDIVISIONS. 



for a great exteut, particularly at Dan vers." It was also stated that 

 " Sienite has not been observed stratified in this vicinity." {I. c, 

 p. 207.) 



The amygdaloidal basalt or melaphyr was called Amygdaloid, and 

 regarded as a rock having a homogeneous base. This base was sup- 

 posed to have been originally cellular, and the cells afterwards fdled 

 with the minerals, " Petrosilex, Quartz, Feldspar, Epidote and Carbon- 

 ate of Lime," forming the amygdules. The base was denominated 

 " Wacke," which in common with petrosilex and basalt was held to be a 

 simple mineral. The amygdaloid was said to be destitute of stratifica- 

 tion, but to present sometimes an imperfect slaty structure. This rock 

 was said to repose on, and to be associated with, the greywacke (con- 

 glomerate) of the vicinity. 



The conglomerate so common in the vicinity of Boston was called 

 greywacke, and said to be " composed of nodules of Petrosilex, Quartz, 

 Argillite, Feldspar, Porphyry, and Sienite ; some of these nodules ap- 

 proach, in magnitude, to rolled masses, and from these we find a grad- 

 ual gradation to grains of sand." {I. c, p. 210.) No stratification was 

 observed in the greywacke and greenstone ; argillite and amygdaloid are 

 said to form beds in the greywacke. The amygdaloid was said to be 

 intimately connected with the greywacke. 



In 1818 there was also published Dr. Amos Eaton's "Index to the' 

 Geology of the Northern States, with a Transverse Section from Catskill 

 Mountain to the Atlantic." 



Like ]\Iaclure and the brothers Dana he follows the Wernerian system 

 in a somewhat modified form, dividing the rocks into five classes : Prim- 

 itive, Transition, Secondary, Superincumbent, and Alluvial. 



He explains the pi-esence of granite boulders in the vicinity of Boston 

 and elsewhere as follows: — 



" The sienite stratum Avas formerly much thicker than at present. This 

 aggregate has been long known to be strongly disposed to disintegration. It 

 has dissolved and set loose the enduring granite, which now lies in loose 

 blocks, with fragments of sienite attached to them, on the surface of the allu- 

 vial deposites." 



This gives us the germ of the theory of the local origin of boulders 

 by disintegration. Beyond this, the finding of a syenite boulder in 

 front of the State House in Boston, and of fragments of argillaceous 

 and graywacke slate near the same city, appears to be all that he 

 knew of the geology of this district. 



In the second edition, under date of 1820, argillite was thought to 



