HISTORY OF GEOLOGICAL SURVEY. 9 



dients are taken from the soil by crops. 5. Best methods of restoring 

 fertihty to exhausted soils, and of improving those that are infertile. It 

 concludes with descriptions of the methods of conducting agricultural 

 operations by several eminent gentlemen, as at the Derby farm on Cow 

 island, Winnipiseogee lake ; the Shaker farm, in Canterbury ; Levi Bart- 

 lett's farm, in Warner ; David Stiles's farm, in Lyndeborough ; Judge 

 Hayes's farm, in South Berwick, Maine, and others. 



The barometrical observations are incomplete, and in a few cases the 

 altitudes have been calculated from them. All that are of value I have 

 had reduced, and given in a list of heights in a subsequent chapter. 



The appendix to agricultural geology contains a large munber of soil 

 analyses, mostly original. 



Geological Map. 



The state authorities did not think it important to color the geological 

 map attached to Jackson's report. Hence it has become difficult to un- 

 derstand many things which otherwise might have been evident. Carri- 

 gain's map seems to have been the topographical basis, with, no doubt, 

 many corrections of town boundaries and various minute points, though 

 the mountains are not reproduced. The scale is exactly half that of 

 Carrigain's. The geological distinctions are the following : i. Granite, 

 sienite and gneiss. 2. Mica slate. 3. Hornblende rock. 4. Argilla- 

 ceous slate. 5. Drift. 6. Alluvium. There are numerous symbols to 

 denote the location of quartz rock, trap, limestone, talc and soapstone, 

 peat, iron, lead, zinc, tin, copper, pyrites, silver, gold, titanium, titanic 

 iron, plumbago, beryl, mica, manganese, arsenic, and molybdenum. Other 

 symbols indicated the place where mines or quarries were worked, the 

 dip and direction of strata, and anticlinal axes. 



Jackson's Theory of Geological Structure. 



These reports and map being chiefly descriptive of mineral localities, 

 it is difficult to deduce from them a very satisfactory notion of strati- 

 graphical structure. In general, he seems to have regarded the rocks of 

 New Hampshire as " Primary," or the oldest to be met with between 

 VOL. I. 2. 



