January 10, 19C8] 



SCIENCE 



69 



base of tlie Paleozoic rocks in the Range 

 Kegion of Arizona is the pre-Tonto, and not 

 the pre-Unkar, unconformity of the Grand 

 Canyon. 



The Tonto sandstone (Cambrian) of the 

 Grand Canyon is probably the equivalent of 

 the Apache group in the Globe District, of the 

 \ Ooleyad©- quartzite in the Clifton District, 

 and, without much question, of the Bolsa 

 quartzite of the Bisbee District. The Tonto 

 shale of the Grand Canyon section apparently 

 becomes more calcareous to the south and is 

 correlated with the Abrigo limestone of Bis- 

 bee. Both carry middle Cambrian faunas, ac- 

 cording to Mr. Walcott. Neither Ordovician 

 nor Silurian is known in the Grand Canyon, 

 nor at Globe nor Bisbee. Mr. Lindgren, 

 however, has found Ordovician at Clifton and 

 some beds of this period may possibly occur 

 in the lower part of the Globe limestone, 

 which is chiefly Devonian and Pennsylvanian. 

 The persistence of the comparatively thin 

 Devonian from the northern to the southern 

 boundary of Arizona is rather remarkable in 

 view of the fact that in the Grand Canyon the 

 Devonian Temple Butte limestone is seldom 

 over 100 feet thick, is lacking in some places 

 and is bounded above and below by uncon- 

 formities. At Bisbee, the Devonian Martin 

 limestone is about 350 feet thick. The Mis- 

 sissippian and Pennsylvanian limestones are 

 both strongly developed at the Grand Canyon 

 and at Bisbee, but the Pennsylvanian has not 

 been found at Clifton. At Globe only Penn- 

 sylvanian fossils have been found but between 

 the Devonian and Pennsylvanian horizons are 

 a few hundred feet of apparently conformable 

 limestones which may in future yield Missis- 

 sippian fossils. 



Fked E. Wright, 



Secretary 



DISCUSSION AND CORRESPONDENCE 



A BETTER METHOD OF PREPARING HERBARIUM 

 SPECIMENS 



Modern critical study and exacting taxon- 

 omic methods require to-day more abundant 

 and better-prepared herbarium specimens. 



These must be made by specialists for special- 

 ists. The private herbarium can no longer 

 be maintained, and the training we give stu- 

 dents must be such as will fit them to do the 

 work the well-organized educational or re- 

 search institutions demand. 



Mere illustrative material in elementary 

 botany beginners should collect in great abun- 

 dance — the profit of their course of instruction 

 depending largely on their assiduity manifest 

 in getting and studying judiciously selected 

 specimens, including, of course, careful ob- 

 servation of the environment and the condi- 

 tions under which the plants occur. This 

 work, in fact, serves well as a preparation or 

 training for collecting and preparing good 

 herbarium specimens. The better knowledge 

 one possesses the better collector he may be. 

 Supposing, however, that the collecting has 

 been properly done and the specimens ready 

 to go in press, we wiU now concern ourselves 

 with the modus operandi of drying. 



The old method of using " dryers " to take 

 up the moisture, substituting dry sheets of 

 the absorbent paper for the moist ones after 

 ten to twenty-four hours, repeating the opera- 

 tion continuously for at least the larger part 

 of a week, is unsatisfactory for two distinct 

 reasons. First, too much labor is required 

 and too much time is consumed ; second, many 

 of the specimens do not become dry quickly 

 enough and therefore lose the fresh life-like 

 appearance and natural color which quick 

 drying generally secures. A better method 

 will reduce the labor, shorten the time, and 

 almost or quite invariably ensure better re- 

 sults. 



Such a method is dependent on an alto- 

 gether different principle, namely, removing 

 the moisture by a current of dry warm air 

 instead of absorbing it by bibulous paper and 

 then promptly removing the latter. It is ex- 

 tremely easy of execution. The ordinary slat 

 press may be used — the sides, however, may 

 be plane boards, or stiff cloth-board, if that 

 is preferred. The pressure is secured by 

 straps or cords in the usual way. 



In place of the " dryers," or rather alter- 

 nating with these, corrugated straw hoards are 

 used. The rolls of such paper, usually found 



