EASTERN MASSACHUSETTS. 401 



Prof. Parker Clcaveland's " Elementary Treatise on ]\rineralogy and 

 Geology" followed Mackire and Godon in the first edition (ISIG), with 

 the addition of the Messrs. Dana's observations in the second edition 

 (1822), and therefore no reference need be made to Cleaveland's views. 



In 1818 was published the "Outlines of the Mineralogy and Geology 

 of Boston and its Vicinity, with a Geological Map," (Mem. Am. Acad., 

 1818, (1) IV., pp. 129-223,) by the brothers J. F. and S. L. Dana. This 

 was, and is, a very important contribution to the mineralogy and lithol- 

 ogy of the region, although it is weak in its petrology and geology, 

 as would naturally be expected from the authors' line of research. 

 This paper probably contains the best account of the mineralogy of tlie 

 region which has yet been written. The general distribution of the 

 rocks was shown on a map, but this is very imperfect. 



The argillite was regarded as the oldest rock known in the region. 

 (I. c, p. 199.) The trappean rocks were called greenstone, greenstone 

 porphyry, and green porphyry ; the last two being regarded as varieties 

 of greenstone. Attention was especially called to the globular disinte- 

 gration of the greenstone, so well marked at some localities in this 

 vicinity. (Proc. Bost. Soc. Nat. Hist., 1877, XIX., pp. 217-237.) They 

 state that the greenstone has not been observed stratified, and that it 

 overlies the argillite. It is also said to occur in large beds in the latter, 

 while it is further claimed that it passes into syenite in places. 



The felsite of the district was divided into two classes : petrosilex and 

 porphyry. The petrosilex was regarded as a mineral, and the tei-m 

 applied only to the compact felsite, e. g. the so-called Saugus jasper. 

 The banding of and irregular colored patches in the felsite were re- 

 garded simply as variations in the coloring of the mineral, and not strati- 

 fication. This to a certain extent agrees with the results of modei-n 

 investigation. Porphyry was the term applied to the felsite, whose base 

 was held to be petrosilex, in which minerals were porphyritically em- 

 bedded, especially quartz and feldspar. The feldspar was said generally 

 to be in " rectangular crystalline grains, and the quartz in small rounded 

 nodules." (/. c, p. 204.) They further state that the "porphyiyis un- 

 stratified in this vicinity, and is intimately connected with Sienite and 

 Petrosilex, into both of which it passes." (/. c, p. 205.) 



The" hornblendic and micaceous granites were classed as "sienite." 

 The rock was regarded as principally a compound of quartz, feldspar, 

 and hornblende, but it was said that " mica sometimes forms a large 

 proportion of the mass ; and hills of Sienite, of a fine structure, con- 

 taining mica in quantity nearly equal to the other ingi-edients, prevail 



VOL. VII. — jfo. 11. 26 



