The Geology of Hingham. 9 



A second table is presented, giving a list of the formations ; 

 the forms of life that appeared in the several periods ; and some 

 general remarks upon the land surfaces, the climatic conditions, 

 and the mountain elevations. Periods not recognized in the first 

 table are presented in this. 



Formations. 



PYROLITHIC 

 TIME. 



ARCHAEAN 

 TIME. 



Azoic Age. 



Eozoic Age. 

 Laureutian 



Period. 

 Huronian 



Period. 



PALAEOZOIC 

 TIME. 



ilurian Age. 

 Primordial 

 Period. 







Canadian 

 Period. 



Trenton 

 Period. 



Note. From lack of definite 

 knowledge of the particular pe- 

 riods in which insect forms first 

 appeared, mention of them is onl_y 

 made after the close of remarks 

 upon other life in the several 

 periods of each Age. 



Indications of Marine 

 Plants and of Protozoa, 

 the lowest of the forms 

 of animal life. 



General Remarks. 



Age of Invertebrates. 



Marine only ; 



Plants, sea-weeds. Ani- 

 mals, all invertebrates. 

 Protozoa, Radiata, Mol- 

 lusca, and Articulata. 

 Trilobites in immense 

 numbers and of mam/ 

 species are found. The 

 largest of these became 

 extinct before the close 

 of this period. Crinoids ■ 

 and Sponges appear. 



Marine only : 



Plants all sea-weeds. 

 Animals, invertebrates. 

 Among Cephalopods Or- 

 thoceras first appear. 



Marine almost entirely. 

 Some late discoveries of 

 land plants have been 

 made in Ohio and Ken- 

 tucky. Animals all in- 

 vertebrates. 



Physical condition making life im- 

 possible. 



The continent in the Eozoic Age 

 was limited to a region mostly 

 within limits of British North 

 America, but embracing, outside, 

 the Adirondack region of N. Y., 

 a region in Mich, south of Lake 

 Superior, a long belt, including 

 the Highlands of N. Y., and the 

 Blue Ridge of Penn. and Va., 

 also areas along the Atlantic 

 Coast in Nova Scotia, Newfound- 

 laud, and Eastern Mass. 



A long but narrow ridge existed 

 along the line where afterwards 

 were raised the Rocky Mountains. 

 Four-fifths at least of the present 

 surface of the continent were 

 under water. 



A mild climate certainly prevailed 

 in the Arctic regions during 

 these periods, as proved by the 

 forms of life found in high north- 

 ern latitudes. 



The Appalachian region, embrac- 

 ing that of the Green Mountains, 

 was one of shallow waters, whilst 

 areas of the rocks of Archasan 

 Time formed islands and reefs. 

 A barrier was thus partially 

 formed, which led the interior 

 continental sea to be compara- 

 tively quiet, where flourished 

 crinoids, mollusks, and corals, 

 the detritus of which made up 

 the growing limestone. This 

 period of physical quiet, Dana 

 remarks, was probably as long 

 continued as " all the time that 

 has since elapsed," a remark cal- 

 culated to impress the mind very 

 forcibly of its duration. 



