136 BULLETIN OF THE 
manifests the several characteristics of an intrusive sheet. It must be 
remembered, too, that of the numerous localities 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 argument 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 
warrants 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. 
NovemBer 16, 1889. 
