146 GEOLOGICAL SURVEY OF THE TERRITORIES. 



of tlie structure of the mountains, more particularly of the eastern slope 

 of the front or main range, were made during the past season. These, 

 though by no means exhaustive, and, in a 'portion of the region, too 

 scattered or imperfect to there define the structure, yet such material 

 as was obtained seems sufficient to indicate certain general features, and 

 a portion of the material from which the inferences regarding the 

 structure are drawn, together with the inferences themselves, are given 

 below. 



Lithological and metamorphic characters are not here regarded as 

 much as they should be in a complete study, nor as much as they may 

 be after the further study of the notes and specimens yet at hand. The 

 accompanying map (Fig. 7) shows the Archaean area over which the most 

 connected observations were made. It is an area extending north and 

 south across the full width of the district, with the main crest of the 

 front range near its western border. The streams along the northern 

 half of the west border belong to the Middle-Park drainage. The main 

 divide passing out from the western border of the map a little south- 

 west of James Peak, comes in again at Gray and Torrey. On the east 

 are the Lignitic beds of the plains in horizontal lining, with the coal 

 horizon and principal masses of terrace gravels approximately shown, 

 followed by the hog-back zone of more or less upturned and eastward 

 dipping Cretaceous, (dotted,) Jurassic shales, (white,) and Triassic red- 

 beds, (heavier horizontal lines.) To the west extends the mountain 

 zone of Archsean rocks to the extreme border of the map. Nearly airthe 

 observed strikes or curves of the rock are indicated by the short dashes, 

 the direction of which show the trend of the strike, while the little mark 

 on one side shows to which side the rock dips, with numbers sometimes 

 attached showing its amount in degrees, the dips being from the hori- 

 zontal. The shorter line extending across the dash indicates vertical 

 strata, with both sides equal, horizontal bedding, and approximate un- 

 certain strikes and dip, seen either at a distance with a field-glass or too 

 small a remnant of structure to be trustworthy, are indicated by the 

 broken dash. A dash may be the result of a single observation of ob- 

 scure structure in granite, or, more often, may indicate the result of a 

 number of observations, or the whole formation may clearly have the 

 given trend, obviously bending here and there as strikes indicate. Re- 

 garding a number of neighboring observations they serve to show the 

 present structure of the region in which they occur. 



Drawing dotted lines through a region so that they are parallel to all 

 the strikes near or abreast of which they pass, they may be considered 

 as indicating, approximately, the course the strike would have if the 

 outcrops could have been traced continuously along them. In other 

 words, the dotted lines represent api)roximately where the continuous 

 outcrop of a horizon, or series of beds, would be if it could be traced. 

 When the structure is clear, or when the observed strikes are rather 

 thickly scattered, these dotted lines may represent an outcropping hori- 

 zon quite closely, but where the observations are more scattered, the 

 course of -the horizon becomes more conjectural, and the line, instead of 

 remaining on its proper horizon, may gradually pass higher up or lower 

 down through the series, while unobserved faults may throw the beds 

 aside and not be indicated by the lines ; yet the latter, though so far 

 incorrect, still serve to connect the observation which would otherwise 

 be too disconnected to the eje, und just so far as the observations go, 

 truly indicate, if approximately, the curves of the outcrops of the folded 

 rocks. An anticlinal, or sjTiclinal, with north and south horizontal SLxis, 

 would thus have the beds outcropping on either side in north and south 



