PHYSICAL HISTORY OF NEW HAMPSHIRE. $3! 



very plainly oozed through crevices in the ossipyte. Evidence of intru- 

 sion at this period is not yet obtained from any other locality ; but, as the 

 lithological character of all the previously erupted members is constant, 

 it is probable that these sienites were all produced simultaneously, most 

 likely at the close of the Labrador period. Thus this age of the world 

 in New Hampshire possessed a fiery character. It was ushered into 

 being by an overflow of igneous material, nourished with ejections of 

 molten rock, and terminated by upheavals, rending of the strata, and 

 pouring of fiery sienite into the crevices, which oozed out and formed 

 mountains. 



The Labrador formation was separated formally from the Laurentian 

 by Sir W. E. Logan, in 1865. It is developed quite differently in Canada 

 from its usual aspect in the White Mountains. Logan estimates the 

 thickness of the anorthosite gneisses of this system at thirteen thousand 

 feet. They are inter-stratified with orthoclase gneiss, quartz, and lime- 

 stones. I do not find, from the descriptions, that there is any great 

 difference in the angle of the dip between the Labrador and Laurentian. 



But there is a closer resemblance between the New Hampshire and 

 the Canadian Labrador rocks, on the north shore of the St. Lawrence 

 beyond the Saguenay river, according to James Richardson. He says 

 the Laurentian gneiss is nearly vertical, with a north-south strike, and 

 much broken, while the Labrador rocks dip at comparatively moderate 

 angles, strike nearly east and west, and are free from contortions and 

 disturbances.* In the Adirondacks, the descriptions of Prof. Emmons 

 would indicate that the labradorite rocks occupy the centre and highest 

 part of the Eozoic area, and, on this account, they bear some resem- 

 blance to the Pemigewasset exposures. 



I think geologists will find my descriptions of the New Hampshire 

 Labrador rocks different from anything that has ever been published. 

 I cannot find any author pointing out areas whose molten granites have 

 been spread out like lava over a considerable tract of country, nor a defi- 

 nite succession of granitic overflows characterized by different mineral 

 composition. The brief itinerary of Mr. Richardson affords a hope that 

 the bleak, northern shores of the lower St. Lawrence will confirm our 

 views of the structure of the Labrador formation, when they have been 



* Geol. Survey of Canada. Report of Progress. 1866-1869, p. 305. 



