MUSEUM OF COMPARATIVE ZOOLOGY. 69 



quarter of a mile, and overlap of almost as much allowance, being made 

 for the missing acute southern point of the western ridge, which is here 

 rounded off. This suggests a fault of the pattern given in case C. 

 Knowing the dip of the anterior trap sheet to be about 10°, the strike 

 of the fault must be east-northeast ; and its heave, 300 feet or more on 

 the southeast. The surrounding topography is very suggestive of such 

 a dislocation ; a view of the oblique gap formed in the ridge as seen 

 when looking southwest from a hill (G) on the west side of the reservoir 

 is given in Fig. 8. 



If the fault extend and maintain its displacement a mile or more to 

 the northeast, it must intersect and dislocate the main trap sheet in the 

 same manner as it has broken, the anterior. Looking along the calcu- 

 lated trend of the fault from the north end of the anterior, we see the 

 gap (7) by which we have come from New Britain, between the north 

 end of High Rock and the high trap ridge (8) next northwest of it, to 

 which no special name is attached. The outlet of the reservoir valley 

 runs through this gap. Assuming that the fault is straight, we have 

 now a better means of determining its direction by sighting the long 

 line from one gap to the qther ; the bearing thus found is N. 60° 

 E., which agrees satisfactorily with that determined by the offset and 

 overlap of the anterior ridge. In further confirmation of the fault, an 

 afternoon return trip may be made from the thrown portion of the an- 

 terior trap ridge, after following it northward half a mile (9), across the 

 strike of the beds toward the thrown portion of the main sheet (8) ; 

 and in so doing, the few shale outcrops that appear are in such close 

 accord with those seen in the morning in corresponding position in the 

 High Rock block that they may be regarded as equivalent beds. Stand- 

 ing on the high ground (10), west of the reservoir, and looking back 

 across the fault valley, the correspondence between the two monoclinal 

 blocks is very apparent, in topography as well as in structure. Rapid 

 advance may now be made on the foundation thus laid. 



Excursion 3. — The Great Fault West of Lamentation 



Mountain. 



A third day may be spent looking for the fault that is supposed to 

 separate Lamentation Mountain from High Rock. It must lie some- 

 where in the country between them. The search may best begin at the 

 point where the cross-section was taken up on the first morning ; but 

 now exploration should be turned westward, descending in the mono- 



