292 ANNUAL OF SCIENTIFIC DISCOVERY. 



US up from any other conclusion than that it is only part — and 

 a rich part — of an already established flora and fauna, lyin*^ 

 undetected at pn'.scnt." His tables show that more than half of 

 the known Silurian speci«'S have liitherto been found in only one 

 locality, <j:iving force to tiic assertion of Prof. Edward Forbes, that 

 a large proportion of all known species of fossils are founded on 

 single specimens. The species thus restricted to a small geograph- 

 ical area also attain onlv a small vertical range or duration in 

 time. As stated l)y the "Quarterly Journal of Science" (January, 

 18G9), "The general law of the range of species in space and 

 time may be broadly and roughly stated as follows: long life and 

 great range; short life and restricted range. Now, without at all 

 doubting the fact tiiat the lives of species, like those of individuals, 

 may vary in length to a great extent, we thiidv that naturalists 

 who "count heads" should satisfy themselves whether a species 

 which has spread over three-fourths of the globe, and enjoyed an 

 existence extending through several divisions of the Siiurian 

 period, is precisely equivalent, in Natural Jlistory value, to a 

 species of the same genus which, with scores of others, was both 

 created and destroyed within the limits of one minor subdivision 

 of the same period, and which never extended beyond an area of 

 a few square miles. To put this question in a concrete form, let 

 us ask whether Orthoceras annidatum is of an equivalent value to 

 0. intermixium? — the former a species ranging from the Caradoc 

 to the Ludlow rocks inclusive, and from New York, through 

 Northern Eurojjc and Great Britain, to Bohemia, while the latter 

 occurs in only one subdivision of the Silurian system, and in but 

 one small district in Bohemia." 



His conclusions are : 1. " We already have materials from al- 

 most all parts of the Silurian scale of rocks to show, with some 

 force, that life began earlier and more abundantly in the vallevs 

 of the St. Lawrence and Mississip{)i than in Euiope. 2. It would 

 appear that the Silurian system of rocks is universal in extent, and 

 that its c(nrii)onent parts were )aid down at a proximate tim(\ and 

 in like manner ceased to be laid down, — stalemtuits approved i)y 

 M. Barrande. 3. It is a very striking fact that the great majority 

 of the Silurian fauna made their first appearance on the same hori- 

 zon ; that is, everywhere on, j)roximately, the same stage or subdi- 

 vision of the epoch. 4. Silurian life was discontinued everywhere 

 at the same time, proximately. 5. The npp(»r Silurian fossils, 

 which people the Prague colonies in fauna D. d., except as they come 

 fiom another area, are not recurrents ; are not the posterity of 

 Bohemian molluscs. The}' are the precursors of an identical and 

 larger coming fauna. Signs are not wanting that they come from 

 a country where the Silurian epoch was more advanced than in 

 Bohemia; and they become of great value by indicating local ine- 

 quality of progress in the act of deposition during tiiis epoch ; sug- 

 gesting, moreover, that any of the Silurian stages mav be in 

 process of formation about the same time with another, in diflferent 

 parts of the world. 



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