2G NEW YORK SPATE MUSEUM 



Small areas of the sediments occur in the interior as far as 40 miles 

 from the borders. In some instances they lie 1500 feet above sea 

 level. They represent mere remnants of once continuous deposits 

 which extended over most if not all of the Adirondacks. There is 

 strong evidence that the submergence of the region was practically 

 complete during Utica time. Since the close of that epoch the 

 region has been above sea level, exposed to weathering and erosion, 

 and has received no deposits except the sands, gravels and clays 

 left by the glacial invasion and the more recent river detritus. 

 - Structural features. The structures of the Precambric rocks as 

 revealed by their present attitudes in the field have not been worked 

 out for the Adirondack region, and even over the limited areas that 

 have been studied and mapped with care the structural details in 

 most cases have proved too confusing to be deciphered. There is 

 abundant proof, however, that the rocks have undergone great 

 compression and have been folded and faulted on an extensive scale. 



One of the principal difficulties encountered in the study of the 

 structural features is the extreme variability as to the evidences 

 afforded by the rocks of their disturbance. The presence of foliated 

 and gneissoid textures is a common characteristic but they are not 

 always so apparent as to be a serviceable guide in the field. 



Foliation is best developed in the dark sedimentary gneisses and 

 schists. These rocks contain a considerable proportion of the ferro- 

 magnesian silicates — biotite, hornblende and pyroxene — which 

 owing to their crystal habit would orient themselves most readily 

 under compression. When the foliation is parallel to the original 

 bedding planes, as seems to be the general case with these rocks, the 

 records of dips and strikes afford unquestionable evidence for estab- 

 lishing the structure. The limestones have flowed and recrystal- 

 lized so that they rarely show either foliation or traces of their 

 former bedded structure. 



In areas underlain by a complex of igneous and sedimentary 

 formations it is seldom that any connected series of dip and strike 

 observations can be made. There is some possibility that in the 

 districts composed mainly of the Grenville series, such as on the 

 west and south, a close study of the field relations may yield positive 

 results. 



The strikes and dips in any part of the region seldom remain 

 uniform over more than a small area. The strike generally follows 

 more or less closely the prevailing trend of the ridges, that is in a 

 direction cast of north, but it is subject to local variations of several 

 degrees. The swings arc gradual as would be expected in folded 



