Aloust 31, 18S3.] 



SCIENCE. 



'291 



son's Bay, the llississippi valley, and the Salt-Lake 

 anil Nevaila basins connnenceJ to sink very early, 

 and the future growth of the continent consisted 

 largely in tilling them up with marine sediments. An 

 inspection of a map drawn upon a correct scale will 

 dissipate the fancied resemblance to the letter V, 

 in the Canadian dominion, so often ieisisted upon. 

 Neither has the development of the land been in 

 bands parallel to the north-west and south-east arms 

 of this supposed angle. A better conception would 

 tiuil three great basins, excluding the unknown re- 

 gii.ns of Mexico and Alaska, in each of which opera- 

 tions were conducted independently. The best 

 known is that of the interior of the United States, or 

 the Mississippi hydrographic basin. This depression 

 wa-i nearly encircled by a crystalline border of high 

 land. Beginning at Alabama, we follow it to New 

 England, thence by a slight gap to the Adirondack 

 promontory, thence across the Lakes to the Dakota 

 promontory. In Minnesota and Dakota the schists 

 are more or less covered by cretaceous clays and ter- 

 tiary sands; but they evidently constitute the floor 

 for the surface strata occasionally piercing through the 

 later deposit, as in the Bl.ick Hills. Thus we may 

 connect the Dakota and Rocky Mountain crystal- 

 lines. From Wyoming southerly the granites are 

 again conspicuous into New Mexico. Thus the cir- 

 cuit is not complete: it is like a horseshoe, with the 

 lower .Mi.«si.-sippi valley in the gap; yet this m.ay have 

 been filled in the Cambrian age, since Laurentian 

 islands are found in Texas, Arkansas, and Missouri. 

 AVe might give reas >ns for believing in the recent 

 origin of the depression between New Mexico and 

 Alabama. 



The map will show, around the borders of this 

 Mediterranean Sea, the primordial sea-beach, wiielher 

 examined in Virginia, New York, Michigan, Colo- 

 rado, or Texas. Could we dissect the land, we should 

 find an immense platter of Cambrian sediments co- 

 extensive with the crystalline highlands surrounding 

 and underlying it. In Canibro-Silurian times the 

 story is repeated. Marine limestones formed other 

 dishes, each limited in size by the upturned edges of 

 the platter underneath. The rest of the history is 

 given in our text-books. Our Mediterranean Sea was 

 not closed till the end of the cretaceous, when the 

 salt-water was expelled, never to return. 



In the west a similar ovoidal, crystalline txirdercan 

 be traced, holding paleozoic sediments. Beginning at 

 tlie Kocky Mountain chain in Wyoming, we follow 

 it southerly to Mexico. Across Arizona are many 

 gneissiu outlines, but not sufficiently numerous to 

 close the gap. In California we reach a country en- 

 tirely gneissic beneath the sands of the desert, which 

 coiniecls with the Sierra Nevadas, and is traceable 

 along the Nevada line nearly to Oregon. There the 

 course is changed, the rocks trend north-easterly, 

 show tliemselves conspicuously in tlie Blue Moun- 

 tains of eastern Oregon, the Salmon Kiver Moun- 

 tains of Idaho, and western spurs of tlie Rockies 

 again in Montana, which are continimus to our start- 

 ing-point in Wycmiing. Our crystallines do not pass 

 north of the parallel of 49° into Columbia. We have 



therefore found a complete crystalline border for the 

 depressions of our western tenitories, and, within 

 this ovoidal line, all the members of the paleozoic, 

 mesozoic, and cenozuic groups, but not arranged with 

 the simplicily of their dislribuiion in the east. 



Less is known of the arctic basin than of the 

 others; but tlie scattered sketches atlordetl by voy- 

 iu;ers indicate the presence of the more important 

 members of the geological column. Where these 

 basins adjoin, there is a much wider area of ancienl 

 land. 



In conclusion, I will simply recapitulate the more 

 important phases of the growth of onr continent. 



We start witli the earth in the condition of igneous 

 fluidity. 



It cools so as to become incrusted and covered by 

 an ocean. 



Numerous volcanoes discharge melted rock, build- 

 ing up ovoidal piles of granite, which change gradu- 

 ally into crystalline schists. When tlnse hills arc 

 high enough to overlook the water, they constitute 

 the beginnings of dry land. 



At the commencement of paleozoic time the conti- 

 nent is composed of three immense basins, loc.ited 

 near Uudson's Bay, the Mississippi hydrographic area, 

 and the great Nevada series of land-lockeil valleys. 



The later history of the development of the conti- 

 nent presents the details of the filling-up of these 

 depressions, the expulsion of the Mediterratiean se.is, 

 and the description of the varied forms of life that 

 successively peopled the land and water. 



The history opens with igneous agency in the 

 ascendant. Aqueous and organic forces became 

 conspicuous later on, and ice has put on the finish- 

 ing touches to the terrestrial contours. The com- 

 pleted structure we must acknowledge to bo ' very 

 good.' 



NOTES AND NEWS. 



Our leading article of June 20 was based in 

 part upon a mistake, wliich we desire to correct. 

 Foreign periodicals received by mail in single num- 

 bers have not been dutiable within the last five years. 

 Nevertheless, the writer of the article, who subscribes 

 to three foreign scientific journals, and receivts them 

 by mail, had been forced to pay duty on each number 

 for the past nine or ten months; and the same has 

 Iwen the case with others of our acquaintance. Our 

 post-office regulations are so frei|uenily changed that 

 one can rarely tell whether he is the victim of a 

 blunder or a whim. 



— M. I'astear, who has jnst obtained a grant of 

 fifty thousand francs from the French Chambers to 

 send a scientific mis-ion to Egypt to investigate 

 whether the cholera be not due to the development 

 of a microscopic animal in the human boily, states, 

 in a letter to Vultaire, the rpiisons which iniluccd hiiu 

 to recommend the board of hcalih to send out the 

 tnission in question. He says, " I urged thesen<ling- 

 out of this nussion on account of the great progress 

 that science has made since the last cholera epidemic 

 respecting transmissible iliscasea. Every one uf Ihote 



