G. W. Hawes—Eochs of the ^^ Chloritic forma' ' '' 



There are varieties of this rock intermediate between these 

 two, some specimens of which are beautifully porphyritic. In 

 some kinds the feldspar is free from impurities ; but in those 

 varieties which are very feldspathic, and the feldspar crys- 

 tals largest, these crystals are quite impure from the envelop- 

 ment of chlorite. The porphyritic rock, from an outcrop near 

 the Orange road, just south of Maltby Park, containing clear 

 crystals of feldspar, was analyzed, and the result is given on the 

 preceding page. An analysis of the diabase of Saltonstall Lake, 

 from my former paper, is added for comparison. 



This "porphyritic ro -k is composed of the same minerals as 

 the more compact varieties, for all of the ingredients can be 

 easily recognized under the microscope. The possible presence 

 of anorthite in the rock is suggested by the following analysis 

 of some large grains of feldspar taken from an adjoining rock : 

 SiO^ 45-52, Al.Og 29-84, MgO 2-35, CaO 15-9'9, NaO 1-61, 

 KO -37, ignition 2-38 = 98-06. This analysis was made by 

 Mr. E. S. Dana some years since, but he states that the micro- 

 scopic examination, and the analysis itself, show that the grains 

 were very impure crystals of a triclinic feldspar, and as all the 

 calculations upon the analyses point to the presence of labra- 

 dorite, we cannot assume that any of the rocks which have 

 been analyzed contain anorthite, though it is very likely to 

 exist in the rocks of the series, since a constant coniposition in 

 the feldspar could not be expected in the diflerent layers of a 

 rock made up of shifting sediments. 



3. Mef.avielaphyre — a specimen taken from an outcrop on 

 Stoeckel's farm is so fine grained as to appear nearly crypto- 

 crystalline; it is broken into angular fragments like some of 

 our trap rocks, and in liict resembles some compact trap so 

 closely as to make it impossible to distinguish it by the eye 

 alone. Its analysis afforded the following results: 

 Metamelaphtbe, fhom Stceckel's Fabm. 



