30 



D. P. PENHALLOW ON TWO SPECIES OF 



From this it appears that the boulder clay is found at about the present level of the 

 lake. Immediately above the boulder clay is a thin layer of soil (A), in which the con- 

 iferous wood was found. Following this are 3.25 feet of gravel and 1.5 feet of peat, con- 

 taining shells. The peat is covered by 1.5 feet of fine sand, in which the oak was im- 

 bedded. The peat (No. 4) includes at the top, shell marl. The shells embrace such forms 

 as those of Planorbis, Limnea, etc,, in all, nine different genera, which Stimpson pro- 

 nounces to be of existing species. The local evidence is such as to confirm the view 

 that the Picea grew upon the spot where found, sending its roots down into the clay. 



The cross section (fig. 2) supplied to Prof Marcy by Dr. E Andrews, shows the posi- 

 tion (S) of the layer of peat, corresponding to No. 4 of figure 1. 



Fig. 2. 



Figure 1 is a section of the lower beach at the point where it is cut by the lake, and 

 about six years ago, bones of the mastodon were found in or on the layer of peat (No. 4) 

 thus exposed. 



Prof. Marcy expresses the view, based upon Spencer on the Iroquois Lake,^ that at 

 the time the Picea grew, the waters of the lake were as low as, or lower than now. The 

 waters afterwards rose and formed the upper beach, then the middle, and finally, the 

 lower beach, which is still in process of formation. At the high level, there was a bay 

 covering Chicago, and an outlet through Lemont. From these data it would appear that 

 the formation is a recent one, and Sir "Wm. Dawson seems inclined to consider it as early 

 post-glacial. 



Descriptions of the Woods. 



Quercus. — The oak is sufficiently well preserved to render good transverse and longi- 

 tudinal sections possible, after treatment with caustic potash. In the transverse section 

 only the general structural features can be made out, with the exception of the thyloses, 

 which are very clearly defined. The wood cells have been so far brought under the 

 operations of decay, as to render it impossible to make out their detailed characters. 

 The same cause, of course, has equally aflected the structure as exposed in longitu- 

 dinal sections ; so much so that it was not possible to obtain satisfactory drawings of 

 the various structural features. Here and there these were made out with sufiicient 

 distinctness to serve as the basis of the description given. 



By comparison with recent species of Quercus, this fossil appears to most nearly 

 approach Q. prinus and Q. garryana, the affinities being nearer the former than the latter. 

 Such differences as could be definitely established, were found in the length of the ray 



' 'Amer. Jnl. Sc' xl, 447. 



