LAURENTIAN SYSTEM. 21 



« 

 between this foraminiferal reef and more recent coral reefs seems to be, that while 

 with the latter are usually associated many shells and other organic remains, in the 

 more ancient one the only remains yet found are those of the animal which built the 

 reef."- 



6. The relatively large amount of potash in the Laurentian series indicates an 

 abundant marine vegetable life, because later fossil fucoidal layers frequently abound 

 in potash, and living algse secrete potash from the ocean in such form as to retain it 

 in the sediments now accumulating, and in which they are buried. 



7. And, negatively, we have no good reason to think the Laurentian Age was 

 lifeless; beside, the actual elements composing the Laurentian rocks are not different 

 from those in succeeding formations; indeed, oxygen, hydrogen, silicon, aluminum, 

 magnesium, calcium, potassium, sodium, iron, and carbon constitute .99 of all the 

 rocks in the world. 



§ 36. The change which sedimentary strata of sands and clays, composed of 

 silica, alumina, and potash, underwent to form granite, gneiss, and mica schist ; the 

 transformation of sand into quartzite, and all other changes caused by crystallization 

 and new combinations, are supposed to be owing to chemical and molecular forces, 

 acting under the conditions of pressure, heat, and moisture. The pressure of a deep 

 sea would develop a high degree of heat. The mountain ranges have undergone 

 volcanic and earthquake upheavals which may have accompanied the metamorphism 

 as active agencies. It would seem to be a law that mountain upheavals follow great 

 sedimentary deposits, and the chemical action is most powerful under the grandest 

 accumulations; but the idea that such accumulations bend the crust of the earth, or 

 the crust of the earth contracts and wrinkles up mountain chains in the act of cooling, 

 is too chimerical for consideration. 



§ 37. Sedimentation ceased when the beds were forced above the ocean, but 

 continued elsewhere. When the beds were elevated, the wear and wash from at- 

 mospheric and aqueous forces began, ^and deposits ensued upon the margin of the 

 land and in the depths of the ocean. The denudation of the anticlinal heights has 

 furnished many geological sections, but the older rocks remain hidden from view, 

 and will forever remain unknown. There is absolute nonconformability of the Lau- 

 rentian rocks with overlying Groups at every locality which has been examined. 

 The Taconic is introduced by total nonconformability, and frequently with a con- 

 glomerate containing pebbles derived from the adjacent Laurentian. Here is an 

 unrevealed chapter of geological history, one that has not been reached and read, 

 and never can be unless some region is unearthed where the Taconic rests con- 

 formably upon the Laurentian. The Laurentian is the home of granite, marble, 

 gneiss, and other valuable building rocks, and the best mica quarries ; but the 

 precious metals have been found only in the intrusive, altered, or sedimentary rocks 

 of later times. 



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