626 
GEOLOGY OF THE FIRST DISTRICT. 
The preceding table, giving the directions of joints and veins, contains but few recorded 
facts, because while making observations over the country under examination, when the 
directions conformed to the general directions of the joints,, they were very, rarely noted. 
Where the rocks are horizontal, the joints are usually vertical; where they are highly inclined, 
one of the sets of joints (usually the west-northwest set) is vertical or nearly so, while the 
other is more or less inclined^ This inclination is usually to the westward where the dip is 
to the eastward. 
The joints, or some of them at least, seem to have been formed previous to the elevation* 
of the strata to their inclined position, and to have exercised an influence in the form and 
position of elevated masses of hills and mountains, as noticed in pages 333 and 334 of this 
volume. 
The causes of these joints are unknown. Various theories'have been proposed to account 
for them, and none of them afford decisive or even very strong evidence of their origin. The 
cause or causes of joints is considered an interesting and important problem, and the deter¬ 
mination of the direction and dip of the different sets of joints over extensive areas in various 
distant regions of the globe may lead to interesting results. Query: Do the same sets of 
joints, prolonged to distant points on the surface of the globe, correspond to great circles V 
2d. If they do so correspond, do they correspond also to any great lines or belts of upheaving 
action ? Or, 3d. Do they correspond to great circles passing through the same axis as that 
along which great upheaving action or derangement, and folding and wrinkling of the strata, 
have heen effected ? These queries are addressed to geological observers, as probable, from 
facts already observed ; and that such effects as we see connected with joints, may probably 
have been produced by subsidence of parts of the earth’s surface and elevation, of others. 
3. Ages of rocks, and periods of elevation and* metamorphic agency. 
(A). Of the ages of the rocky strata, from the Potsdam sandstone, the lowest sedimentary 
and fossiliferous rock of which we have any knowledge, to the conglomerate of the base of 
the Coal formation, there is no doubt. The rocks are well developed, and fairly exposed to 
observation in numerous places where they have been examined, and are found in superposition 
as they have been described in this volume, and in the final geological reports by Professors 
Emmons and Vanuxern. 
The TAcoNic ROCKS have been discussed as imperfect metamorphic rocks. Vide pp. 
422, 438. 
The UPTURNED SLATE AND GRIT LIMESTONE, etC. ROCKS OF THE HUDSON VALLEY, have 
been identified with the horizontal ones of the Mohawk valley (Vide pp. 377, 378) on the one 
hand, and their passage into the Taconic rocks of the other rendered highly probable (pp. 
422, 438). 
The UPTURNED ROCKS OF Bellevale, Skunnemunk, Goose-pond, etc. mountains, and 
of Townsend’s iron mine and Pine hill, have been referred to the rocks of the Ontario 
division. (Vide pp. 362 to 366.) 
