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



The order of succession adopted by Emmons was the order 

 of superposition, as he states, with arguments in its favor, on 

 page 147 of his report, the idea of flexures being rejected. 

 The granular quartz he says (p. 138) '* lies between two masses 

 of limestone," — which is topographically a fact. 



The idea of the pre-Potsdam age of the beds was based on 

 the absence of fossils ; on the difference in the kinds of rocks, 

 and in their succession, from the lower rocks in the JSTew 

 York series ; also on supposed unconformability, no special case 

 however being mentioned. He says, with reference to the distinc- 

 tion in kinds of rocks (p. 139), " As a general rule, certain 

 minerals are found in particular rocks ; and may not a similar 

 rule or law prevail where a system of rocks is concerned ?" 



Early in May of 1844, two years after the appearance of 

 Prof. Emmons's Report and over half a year before his second 

 presentation of the system, Professor H. D. Rogers brought 

 the Taconic question into his Presidential address before the 

 u Association of American Geologists and Naturalists," and 

 reiterated his former conclusions.* 



18 1& to the close of 181$ ; Phase II — In December, 1844, 

 appeared as a pamphlet in 4to — the preface bearing the date 

 December 2, 1844 — Prof. Emmons's revision of the Taconic 

 system, with additions and an extension of its limits ; and in 

 1846, the same was published as a chapter in his 'N. Y. Report 

 on Agriculture. The prominent changes are the following : (1) 

 the system is, for the most part, turned the other side up, 

 Rogers's views being adopted as to flexures and overthrust 

 folds. (2) It is made in part fossiliferous, and the fossilifer- 

 ous part is put at the top under the idea that the fossils proved 

 it to be the newer part. (3) The granular quartz is placed at 

 the bottom. 



The order of the strata in the Report, and the equivalents, 

 are as follows : 



Taconic System of December, 1844. Equivalents. 



j a Black slate (Bald Mt.) I. Cambrian. 



K (b Taconic slate. 'Ill, I. Hudson slate and Cam- 

 brian. 



4. Sparry limestone. II. Lower Silurian. 



3. Magnesian slate. III. Hudson slates. 



2. Stockbridge limestone. II. Lower Silurian. 



1. Granular quartz. I. Cambrian. 



* H. D. Rogers, this Journal, xlvii, 137,247, 1844. The address is a discus- 

 sion of geological views, and is of permanent interest. His remarks on the 

 Taconic system occupy pages 150 to 153; and he ends them with the suggestion 

 that the Taconic system, instead of belonging exclusively to the Champlain 

 division, may "include also some of the sandy and slaty strata here spoken of as 

 lying beneath the Potsdam sandstone," referring to his own observations in 

 Virginia and East Tennessee. 



