36 'I'll* Anuria* a Geologist July, 1S94 
of faults, namely, those resulting from vertical movements, 
and those resulting from horizontal movements in the earth's 
crust. 
None of the above classifications takes into account the in- 
clination of the crest and trough lines, or in other words the 
pitch, of folds of strata, and it is evident that a new type of 
fault is found if the pitch of folds is different in the two 
limbs of an inclined strike fault. An instance of this kind 
I have recently described from the southern extension of the 
Green mountains in Massachusetts and Connecticut.* The 
fault described is a strike fault and one resulting from hori- 
zontal movements. Its course is roughly north-south, follow- 
ing for n considerable distance the direction and approxima- 
ting the position of the Housatonic river. It has an inclined 
hade uniformly east, throughout the twelve miles that it has 
been studied. Throughout this distance no noticable pitch 
of the folds is observable to the eastward of the fault line and 
consequently a single horizon — the Canaan dolomite — is ex- 
posed. A steep northerly pitch, however, characterizes the 
folds to the west of the fault line, so that not only the Canaan 
dolomite but two superior beds — the Riga schist and the 
Egremont limestone — appear along the fault line to the north- 
ward, and two inferior beds — Cambrian quartzite and gneiss 
— lie along it to the southward. For a part of its course Ca- 
naan dolomite lies on both sides of the fault Mne. Some- 
where within this stretch of the fault line is a point at which 
there has been no displacement, but about which the western 
limb of the fault has suffered a differential movement like 
that of a lever about its fulcrum. As the arm to the north 
has been depressed, that to the south has been elevated. It 
is therefore only to the northward of this point that the fault 
is of the true reversed type. To the south of the fulcrum 
point the relations observed to the north are reversed. The 
eastern or hanging wall is downthrown and the western or 
foot wall is upthrown. These relations correspond to those 
of the normal fault, since a vertical line would penetrate any 
given horizon but once. The amount of throw increases pret- 
*Wm. H. Hobbs,.On the geological structure of the Housatonic val- 
ley Ivingeasl of naounl Washington. Journ. ofGeol., vol. I. pp. ?!i:!-;!ts. 
(Nov.-Dec, I89i 
