

GEOLOGY. 



iKto much smaller fields.than those into which 

 they are at present generally divided. 



Green Sand Formation. This formation is 

 found under the chalk. It is formed of a va- 

 riety of beds : the upper beds near the chalk 

 have a green or grayish colour, the lower beds, 

 which are commonly much thicker, vary in 

 colour, from yellow to brown and red. It is 

 composed of silicious sand, mixed with mica 

 and chlorite. "The means of permanently 

 improving this soil," says Mr. Morton, " after 

 it is drained and enclosed (if for pasture), are 

 so immediately within the reach of the farmer, 

 that he can at little comparative expense im- 

 prove its texture, and permanently increase its 

 productiveness, by chalk or chalk marl, on the 

 one hand, and the oak or clunch clay, on the 

 other; but even without the application of 

 these substances, deep or double ploughing or 

 trenching has the effect of deepening the soil, 

 and increasing its capability. When mixed 

 with the chalk marl above it, it has the power 

 of receiving and transmitting moisture more 

 freely, and is neither so easily injured by wet 

 weather, nor by excessive droughts, as other 

 soils are." (On Soils, p. 43.) 



(limit has commonly a bluish or gray aspect, 

 and its geological position is in the centre of 

 the green sand formation : the two greatest de- 

 >f it, in England, are in the Vale of White 

 B MI Berkshire, and in the counties of 



Cambridge and Huntingdon. It is found at South 

 Mar-tou, in Wiltshire, at Wantage, Thame, 

 through Bedfordshire to Caxton and St. Ives. 



Before the year 1807, although mineralogy 

 had received some attention in the United 

 States, little or nothing had been done towards 

 ascertaining its geological features. At that 

 time William Maclure commenced the task, 

 and single-handed, made a progress which re- 

 flects the highest credit upon his memory, for 

 he developed the leading characteristics of the 

 rock formations, in doing which, he crossed the 

 Alleghany mountains in fifty places. 'Ha- 

 state geological surveys which have been car- 

 ried on for several years past, and are still 

 prosecuted, seem to be enterprises peculiarly 

 American, having preceded those regularly 

 undertaken in any other country. The annual 

 reports of these surveys have dwelt much upon 

 economical geology, and placed an immense 

 ina^ of minute and accurate information be- 

 fore the public, which cannot fail to be profita- 

 ble to agriculture and other useful objects. 

 North Carolina has the honour of having first 

 directed a survey of her territory, a duty per- 

 lormed by Prof. Olmsted, whose reports were 

 made in 1824, 1825; since then, South Carolina 

 has been geologically explored byProf.Vanux- 

 u;n. These two Southern States were succeed- 

 ed by Massachusetts, the last report of which, by 

 Prof. Hitchcock, was made in 1837. Tennessee 

 has been explored by Prof. Troost; Maryland 

 by Prof. Ducatel; New Jersey and Pennsylvania 

 by Prof. H. D. Rogers ; Delaware by Prof. J. C. 

 Booth ; New York by Profs. Vanuxum, Mather, 

 Emmons, and Mr. James Hall; Virginia by 

 Prof. William B. Rogers ; Maine, Rhode Island, 

 and New Hampshire, by Dr. Charles T.Jackson; 

 Connecticut by Dr. J. G. Percival and Prof. C. \ 

 U. Shepard Ohio by Prof. Mather, assisted by ; 



GEORGIA BARK. 



Dr. S. P. Hildreth, and Profs. Locke, Briggs, 

 and Foster; Michigan by Mr.D. Houghton; Indi- 

 anna by Dr. D. D. Owen ; and Georgia by Mr. 

 J. R. Cotting. It thus appears that within the 

 last 16 or 17 years, surveys have been com- 

 menced, and most of them completed, in 19 

 states and two territories of the Union, em- 

 bracing an area of nearly 700,000 square miles, 

 and that for some years past not less than 25 

 principal geologists, and 40 assistant geolo 

 gists, have been almost constantly ensured 

 under the patronage of the state governments, 

 in the examination of the various parts of the 

 Union. The British provinces of New Bruns- 

 wick and Nova Scotia have also been geologi- 

 cally examined by Dr. Gessner, whilst the ex- 

 ploration of Canada has been commenced un- 

 der the superintendance of Mr. Logan. Much 

 of the materiel thus amassed cannot fail to be 

 of high interest in an agricultural point of 

 view, as pointing the situation and exact value 

 of soils, and the invaluable beds of mineral 

 fertilizers, in the form of lime, marl, green 

 sand or silicate of potash, &c., &c. 



From such facts as these the farmer will 

 readily perceive that the science of geology is 

 not without its material and extensive value to 

 the tiller of the earth. It enables him at least 

 to cultivate his soils on solid data, to avoid the 

 adoption of idle and fruitless modes of cultiva- 

 tion, to pursue that which the situation of the 

 strata he tenants determines to be the best. It 

 is no reason for the neglect of its assistance 

 that other sciences can perhaps do more for 

 the farmer; and even the objection, though 

 very common, amounts, in fact, to an admis- 

 sion that geology t* a science capable of ren- 

 dering services to acrriculture. (Prande's Ler.t. 

 on Geology ; Morton on Soils ; Davy's Elem. Jlg 

 ('firm.: Paris on the Soils of Cormcall; J. F. 

 Johnston's Lee. Cherti. and GeoL; Prof. H. D. Ro- 

 ger's Geological Surveys of Pennsylvania, and New 

 Jt'rxnj : Prof. C. J. Booth's Survey of Delaware ; 

 Professor Jackson's Survey of Massachusetts; 

 Geological Survey of New York ; Dr. Ruffin's 

 Survey of North Carolina, fyc. t $r.) 



GEOMETERS. A species of caterpillar. 

 See SPAN-WORMS. 



GEORGIA BARK (Pinckneya pubens'). "This 

 tree," says Michaux, the younger, " still more 

 interesting by the properties of its bark, than 

 by the elegance of its flowers and of its foliage, 

 is indigenous to the most southern parts of the 

 United States : probably it grows also in the 

 two Floridas and in Lower Louisiana. My 

 father found it for the first time in 1791 on the 

 banks of the St. Mary. He carried seeds and 

 young plants to Charleston, and planted them 

 in a garden which he possessed near that city. 

 Though intrusted to an ungrateful soil, they 

 succeeded so well, that in 18071 found several 

 of them 25 feet high, and 7 or 8 inches in dia- 

 meter; which proves that the vegetation of 

 this tree does not require a very warm climate, 

 nor a very substantial soil. 



" With a great affinity to the cinchona which 

 yields the Peruvian bark, my father discerned 

 in the Georgia bark sufficient differences, to 

 distinguish it as a new genus. In testimony of 

 his gratitude and respect, he consecrated it to 

 Charles Cotesworth Pinckney, an enlightened 



535 



