SEARS'S SUPPLEMENTARY REPORT. lH 



Revised scheme of numbers. 



(-(-) Hornblende gr.-mite. 



(12) Eruptive porphyritic gneiss. 



(18) Cambrian rocks. 



(19) Carboniferous rocks. 



GEOLOGICAL SUCCESSION OF THK KOCK FORMATIONS OF 



ESSEX COUNTY, MASS., FROM THE EARLIEST TO 



THE MOST RECENT. 



Archean, Laurentian gneiss, schists and sandstones, all 

 crystalline, more or less contorted and highly metamorphic. 



Pre-Cambrian, Arkoses, Hornblende epidote gneiss, 

 Limestones, folded and metamorphic. 



Lower Cambrian (Paleozoic) conglomerates, quartzites, 

 slate and limestone, Georgian Olenellus, etc. 



Eruptive (igneous) rocks, muscovite biotite granite. 



Hornblende granite. 



Hornblende biotite granitite. 



Eruptive porph3ritic gneiss. 



Quartz augite diorite. 



Quartz hornblende diorite. 



Essexite nepheline rock and aegirite ditroite schieffer. 



H(»rn])lende diorite. 



Elaeolite zircon syenite and augite nepheline syenite. 



Hypersthene augite basalt dyke rocks (eobasalt). 



Augite olivine basalt dyke rocks. 



Diallage gabbro dyke rocks. 



Diallage augite olivine gabbro dyke rocks. 



Aegirine Tinguaite d3'ke rocks. 



Aegirine syenite dyke rocks. 



Ancient volcanic rocks, rhyolite breccias, banded 

 rhyolite, corhyolite. 



Hornblende diorite dyke rocks. 



