56 Loughlin and Hechinger — Unconformity 



earlier age than the Sterling and its equivalents, the area 

 affected by the upheaval accompanying the intrusion of latter 

 granites will not be diminished, and the earlier granites must 

 be regarded as remnants of older batholiths which escaped 

 obliteration within the area affected by the latest batholith.* 

 Such relations, of course, are possible, but have not been 

 proved. The hypothesis of a single complex batholith is 

 entitled to quite as much consideration, and, if proved by more 

 extended and detailed work, will go far towards clearing away 

 several of the stratigraphic and structural complications which 

 have persisted under the multiple batholith hypothesis. 



That the single batholith hypothesis is far from impossible 

 may be shown by comparison with igneous rock areas in the 

 West. Igneous rocks, both intrusive and effusive, extend over 

 much of the Cordillera and represent a great variety of types, 

 from very acidic to very basic, and from subalkaline to alkaline. 

 These were mostly erupted within an interval between late 

 Cretaceous and early to middle Tertiary time, and, in some 

 restricted areas, within narrower limits. As they accompanied, 

 or closely followed, the Laramide revolution, there was in 

 the West a period of extensive upheaval and complicated 

 igneous activity within a short interval of geologic time — late 

 Cretaceous to early or middle Tertiary. In the Sierra Nevada, 

 the plutonic rocks, consisting largely of granodiorite but rang- 

 ing from granite to gabbro, are intrusive into steeply dipping 

 Jurassic slates, but are distinctly older than lower Cretaceous 

 beds. Both upheaval of the Jurassic slates and the extensive 

 intrusion of the igneous complex took place within the interval 

 between late Jurassic and early Cretaceous. It is, therefore, 

 demanding no excessive speed of geologic processes to hold the 

 view that all the granites within the small portion of New 

 England under consideration were erupted during the interval 

 between late Pennsylvanian and early Permian. Attention 

 may also be called to the extensive igneous activity which 

 existed throughout a large part of Europe during late Car- 

 boniferous and early Permian time. In fact the deformation and 

 igneous activity which took place between the deposition of 

 the " Coal Measures " of Rhode Island and the Dighton con- 

 glomerate give to the area under consideration a European 

 rather than American character. 



*In this case, the earlier biotite granites may prove to be the equivalents 

 of the granite along the northeast half of the Maine coast, which has been 

 determined to be of Devonian (?) age. U. S. Geol. Survey Geol. Atlas, 

 Penobscot Bay folio (No. 149), 1907 ; or they may be correlated with the 

 Taconic revolution, as stated by C. H. Clapp. (The igneous rocks of Essex 

 Co., Mass.: abstract of thesis presented in part fulfillment of degree of 

 Ph.D., Mass. Inst. Tech., Boston, Mass., 1910.) Dr. Clapp's detailed discus- 

 sion of the granite problem is awaiting publication. 



