REVIEWS AND BOOK NOTICES. 241 



the Ozark Mountains ; which formed an archipelago in the palaeo- 

 zoic sea, and are now from 300 to 700 feet above the limestone at 

 their base. The Pilot Knob group includes four of these, and the 

 Iron Mountain is another and distinct mass. All of these consist 

 wholly or in part of quartziferous porphyry or orthophyre, but in the 

 vicinity of these porphyry hills are others composed of granites, 

 often chloritic or hornblendic, some of them capped by the porphyry 

 wfiich is considered as a newer rock, and, it is suggested by Pum- 

 pelly may be the youngest member of the Eozoic (Archaean) rocka 

 of the region. He, however, adds in a note that the red granites 

 may be an exception to this supposed rule. These porphyries pre- 

 sent some considerable variations in character, but may be described 

 as having a fine grained compact base or matrix with conchoidal 

 fracture, composed of an intimate mixture of feldspar and ouartz, 

 in which are generally disseminated small crystalline grains of vit- 

 reous quartz, and crystals of pink or white feldspar, generally tri- 

 clinic. The colors of this rock are various shades of yellow, red r 

 gray, brown and black, and it is often banded in its structure, 

 sometimes exhibiting thin layers, occasionally with alternations 

 of quartz, in addition to which, according to Pumpelly, it is strat- 

 ified on an immense scale. Epidote, chlorite and a steatitie min- 

 eral occasionally occur in it, and magnetic and specular iron ores 

 are often disseminated through the mass. To those familiar with 

 the geology of our eastern coast it is only necessary to say that 

 these porphyries seem to be identical with those of Lynn, Saugus, 

 Marblehead and Newburyport, Massachusetts, which are traced 

 thence along the coast of Maine and New Brunswick, and are well 

 developed about Passamaquoddy Bay, where they occasionally 

 contain small deposits of iron ore. These porphyries have already 

 been compared by Hunt with those of Missouri and with similar 

 ones on the north shore of Lake Superior. As seen on the coast 

 of New Brunswick, they are, according to him, intimately associ- 

 ated and interstratified with schistose rocks, supposed to be of 



At Pilot Knob, the excavations in the ore-deposit have exposed 

 a considerable section of the strata, which dip at a moderate angle 



banded porphyry, one of these containing iron ore in grains and 



