92 GEOLOGICAL AND MINERALOGICAL NOTES. 



and where oiie of these Joint structures twenty-five feet 

 thick has disinteo^rated and eroded on its outside leavinof 

 a nucleus we may expect to find boulders like Ship Rock 

 and others of similar size in its neighborhood. These 

 eroded boulders of granite at Peabody, Beverly, Man- 

 chester, Gloucester and Rockport form the entire basis of 

 the so-called "Frontal moraine theory " of which, after a 

 careful examination of the region, I find not the slightest 

 evidence ; indeed, there are no erratic boulders in the whole 

 region. Those which have been considered as such are 

 clearly fragments of dyke masses which cut the granite. 

 Several forms of coarse diorite, syenite, feldsite and gab- 

 bros cut these granites in various directions, and nearly 

 all of them have become in part somewhat schistose and 

 stratified by alteration making a great variety of forms. 

 Now what is more natural than that we should find frajr- 

 ments formed from these dyke rocks mixed with the gran- 

 ite boulders of the region in which they are found in situ. 



In the early spring I pointed out several examples of 

 these disintegrated ledges of granite syenite and diabase 

 to Mr. John L. Gardner, 2nd, of Boston, and also the Lac- 

 colite dykes at Beverly. These he kindly photographed for 

 me and as they illustrate my work on this disiiitegration 

 in situ they are extremely valuable additions to the geol- 

 ogy of Essex County. 



The so-called syenite of Moulton's point, South Salem, 

 is a true granite, composed of quartz, orthoclase, feldspar 

 and glaucophane. This glaucophane is the blue horn- 

 blende, considered as rare by Professor Rosenbusch, de- 

 scribed and analyzed by Professor Bodewig from specimens 

 coUected on the Island of Syra and the Zermatt. Accessory 

 minerals are calcite, apatite, biotite mica, magnetite iron 

 and an abundance of zircon crystals. I would suggest for 

 this form of granite the distinctive name of zirconiferous 

 glaucophane granite. 



