MUSEUM OF COMPARATIVE ZOOLOGY. 73 



with drift that no further sign of the fault has been found there ; there 

 are, however, indications that it is extended a number of miles beyond, 

 even to the intrusive sheet of West Rock and Gaylord's Mountain. Be 

 this as it may, there can remain no more doubt as to the existence of a 

 fracture between the Lamentation and the Hanging Hill blocks. This 

 fracture we shall call the " Great Fault." 



Excursion 4- — Faiilts south of Lamentation Mountain. 



It was noted above that the occurrence of a number of faults systema- 

 tically arranged might be taken as further evidence in favor of the fault 

 theory as against the theory of repeated deposits. A fourth day may there- 

 fore be spent in searching for them. The first guide in the search will 

 be, as has already been suggested, the gaps in the line of the main trap 

 ridges. One of these gaps appears at the southern end of Lamentation, 

 dividing it from Chauncy Peak. If a fault run between them, it must 

 dislocate the anterior ridge also. Walk, therefore, to a point (1) Fig. 9» 

 on the anterior ridge of Lamentation, a little south of the ash-bed that 

 was visited on the first excursion. To the north, we know the ridge is 

 continuous as far as the Great Fault. To the south, a short walk brings 

 us to a little notch by which a small stream escapes from the anterior 

 valley, and beyond which the ridge is continued in the same line as be- 

 fore ; the notch must therefore be regarded as a simple transverse water- 

 cut. But on following the ridge a little farther, it ends (2) on the 

 northern side of an open meadow, and crossing here to the south noth- 

 ing but conglomerate (3) is found, and with such strike as would if pro- 

 longed northward carry it directly to the trap. The fault between Lam- 

 entation and Chauncy may therefore probably pass by the southern 

 end of the anterior thus determined. A bearing taken from the south- 

 ernmost point of the anterior trap to the gap (8) at the south end of 

 Lamentation reads N. 60° E., and this is within a few degrees the same 

 as the bearing of the faults already described. As a further test of 

 the occurrence of a fault here, the northern end of the anterior to the 

 Chauncy Peak block should be found somewhat to the north of the 

 southern point of the anterior to Lamentation. It is found (4), pre- 

 cisely as predicted, lying at appropriate distance in front of Chauncy 

 Peak, containing an ash-bed with bombs of lava (5) like those already 

 described in the anterior of the Lamentation block ; and it ends directly 

 under the southern blufi" of the main sheet (6) in the northern block. 

 A few shale outcrops are found on its back, and others appear on 



