410 J. D. Dana — Brief history of Taconic ideas. 



wider regions of absorption is continued till these intermediate 

 regions of transmission disappear, the whole, to repeat an ex- 

 pression I have used in an earlier memoir, seems to become 

 one continuous cold band, in which, however, we have found a 

 little heat struggling through in the part beyond 11^. Briefly, 

 then, we may say, that to an eye which could see the whole 

 spectrum, visible and invisible, the luminous part being, as we 



know, interrupted by occasional dark lines, the lower part to 5^ 

 would appear to consist of alternate bright and dark bands, and 



the part below 5^ be nearly dark, but with feeble " bright " 

 bands at intervals. In conclusion, we may say that these new re- 

 searches extend the known solar spectrum from three to much 

 over the eighteen microns, shown on our plate, and while con- 

 firming the previously announced fact that the solar heat of 

 the great wave-lengths which actually reach us is negligible in 

 amount, show from the fact of the existence of any at all, that 

 the anomaly of our being able to perceive lunar heat where we 

 could not formerly detect solar, can be explained consistently 

 with the possible existence of the latter of every wave-length 

 before absorption. 



These investigations into a problem of Solar Physics have 

 also incidentally led us to the prospective means of solution of 

 an important one in Meteorology, for they have opened to 

 observation the hitherto unknown region of the spectrum, in 

 which the nocturnal and diurnal radiations not only from the 

 moon toward the earth, but from the soil of the earth toward 

 space, are to be found and may be hereafter studied in detail. 



Akt. XLII. — A brief history of Taconic ideas ; by James 



D. Dana. 



As the Taconic controversy is now nearing its end, a brief 

 review of the progress of ideas relating to the various sides of 

 the subject from the time of the earliest discussions to the pres- 

 ent will be found instructive.* 



* A historical account of the Taconic, especially of the views of Taconic advo- 

 cates, entitled " The Taconic System and its position in Stratigraphical Geology," 

 by Mr. Jules Marcou, is contained in the Proceedings of the American Academy 

 of Sciences, vol. xii, 1884, 1885, pages 174 to 256. It relates mainly to the 

 " Upper" Taconic, and makes little mention of facts or observations of the thirty 

 years past connected with the "Lower" Taconic rocks in the southern half of 

 Vermont, Massachusetts with its typical Williamstown Taconic section, and in 

 eastern New York from Rensselaer Co. southward ; all which have a profound 

 bearing on the question of age, and on the true relation of the " Upper " and 

 " Lower" sections. No account is given of the Taconic system of 1842, in the de- 

 tailed presentation of which Prof. Emmons states its fundamental and distinctive 



