PLANT BEDS OF BUCK PEAK AND THOMPSON CREEK 371 



The Mesozoic plant localities considered in this paper are shown in 

 figure 1. 



Plant Beds of Buck Peak and Thompson Greek, Oregon 

 composition and attitude 



The plant beds of the Buck Peak region are best exposed along Thomp- 

 son creek, where, as shown on the accompanying sketch map, figure 2^, 

 they form a belt a mile in width. They are composed very largely of 

 conglomerate, with a small proportion of sandstone and shale at the top, 

 where fossil plants are most abundant. The general dip is to the west- 

 ward at an angle of about 38 degrees, and a great thickness of strata, pos- 

 sibly more than 1,000 feet, is well displayed. At least three-fourths of 

 the whole mass, its lower — that is, older — portion, lying upon the eastern 

 side, is conglomerate, and it is composed for the most part of greenstone 

 pebbles apparently derived from the mass which limits the conglomerate 

 on the east. This is especially true of the basal portion. In the middle 

 and upper portions of the conglomerate pebbles of chert, sandstone, and 

 conglomerate become more abundant and finally predominate, making a 

 conglomerate like much of that in the "Myrtle formation." Small beds 

 of sandstone and shale occur locally throughout the basal conglomerate, 

 and some of them contain distinct traces of leaves, showing that the 

 greater part and possibly the whole thickness of the conglomerate belongs 

 to the plant beds. 



The first leaves were found in this section, in a thin bed of shale 

 within massive sandstone, a short distance below the dam, but the prin- 

 cipal leaf locality is 75 feet higher in the succession, in the basal portion 

 of the sandstone and shaly sandstone which forms the upper 180 feet of 

 the exposed section and passes unconformably beneath the Eocene. In 

 this section the youngest of the plant beds is covered by the Eocene. 



LITHIFICATION AND VEININQ 



The sandstones and conglomerates of the plant beds are not so firmly 

 lithified as to break with a smooth fracture surface through the grains or 

 pebbles, and in this respect are more nearly like the average of the Knox- 

 ville beds than of the Dothan. None of the beds were found with evident 

 siliceous cement, although a few small but distinct veins were observed. 



2 This map, prepared originaUy from Land Office plats and modified by criticisms In 

 the field, still has many inaccuracies, but is the best means yet available for showing the 

 areal distribution of the various formations. 



