136 BULLETIN OF THE 



manifests the several characteristics of an intriisive sheet. It must be 

 remembered, too, that of the numerous locaUties instanced on the east- 

 ern ranges, all (with one exception, Hartford) belong to only three 

 extrusive sheets ; and hence the evidence that is found at one point 

 supplements or confirms that found at another in a most satisfactory- 

 manner. All this seems to us to be beyond explanation either by acci- 

 dental coincidence or mistaken identification. While judgment might 

 well be suspended if our argument rested on single examples, or on nu- 

 merous examples confusedly arranged, it is difficult, even if necessary, to 

 maintain an open mind -in the face of evidence at once so full, so varied, 

 and so accordant. If all the trap sheets of the region were of one 

 kind, the ai'gument would be weakened ; for in the absence of either 

 kind of sheet, the peculiarities of the other would not be illumined by 

 the light of contrast. The presence in the single region under consid- 

 eration of sheets with the features of intrusions and extrusions there- 

 fore greatly increases the confidence that one may feel in the case, and 

 waxTants the acceptance of those sheets that we have called extrusive 

 as conformable and contemporaneous members of the Triassic series, by 

 means of which the dislocations of the formation can be detected. 



The fullest statement of the method by which the extrusive trap 

 sheets can be thus employed is given in the article above referred to,^ 

 by the senior author, in which the process of investigation followed by 

 the advanced section of the Harvard Summer School of Geology during 

 a week's work about Meriden is presented in detail. It is now our 

 design to continue the investigation in the district northwest of Hart- 

 ford, where a preliminary excursion has indicated a change in the course 

 of the faults from the uniform northeast trend that they possess in the 

 Meriden district. When the faults are mapped out over a considerable 

 area, comparison can be made between their course and the strike of the 

 schists on either side of the Triassic valley, on which the course of the 

 dislocations is thought to depend. 



1 The Faults in the Triassic Formation near Meriden, Conn., Bull. Museum Comp 

 Zool., Geol. Series, I., 1889, pp. 61-87. 



NOVEMBEK 16, 1889. 



