and subsequent to the folding of the Laramie Group, as here exposed, there must have been a period of erosion. I will refer to this again. Smith's Fork and Bear River Region.-Along the east side of Bear River, between the valley and the bounding mountains, is a comparatively low area filled with gray and greenish-gray sandstones, which sometimes form low hogbacks. These rocks are folded conformably with the underlying older beds, and extend northward along Smith's Fork and Salt River into the region of Snake River, where they are beyond the limits of our district.

On Twin Creek, a branch of Bear River, joining it from the east, these sandstones are seen dipping to the westward 40 or 45°, and contain coalbeds, in connection with which the following fossils were found:

Corbicula (Veloritina) durkei.

Rhytophorus meekii.

Goniobasis chrysaloidea.

Goniobasis chrysallis.

Volsella (Brachydontes) sp.?

Pyrgulifera humerosa.

Membranipora ?
Ostrea sp.?
Neritina sp.?

Resting on the beds containing these fossils were the red Conglomerates of the Wahsatch Group, dipping to the eastward about 50. This is about the same unconformability noted on the west side of the Green River Basin.

On Smith's Fork of Bear River, three miles above its mouth, and about twenty miles north of the Twin Creek locality, coal-beds again occur in gray sandstones and contain Unio vetustus and other obscure Laramie forms. Twenty miles farther north is another fossil locality, from which the following were obtained:

Corbicula (Veloritina) durkei,
Corbula pyriformis.
Goniobasis chrysaloidea.

Goniobasis cleburni.

Pyrgulifera humerosa.
Unio vetustus.

Ostrea sp.?

The more northern extension of these beds was not carefully traced, but it was evident that they form a large part of the surface between Salt River Valley and the Blackfoot region south of Snake River.

GENERAL REMARKS.

The bottom of the Laramie Sea appears to have been subjected to a constant and gradual subsidence, as the character of the strata indicates

their deposition in shallow waters, and the thickness attained is from 3,000 to 5,000 feet.

The lower sandstones are similar to those of the Fox Hills Group of the Cretaceous, and the two formations are conformable. As far as noted, the conformability extends from the Carboniferous to the top of the Laramie Group, as exposed in the district under consideration.

There were some indications in Ham's Fork Cañon that the Laramie Group rested on the upturned edges of the Triassic Red Beds, but the relations were obscure, and all other occurrences seemed to indicate that the Laramie Group is conformable to the underlying formations.

It should be stated here that the western shore-line of the PostCretaceous has not been identified, and that it is probable that if the peripheral portions of the Laramie Group could be observed, as Dr. White remarks, some unconformity would be seen between it and the Fox Hills Group. He says: "There must necessarily be some unconformity between these groups in the peripheral portions of the Laramie, because, as will be shown farther on, the area upon which its waters rested was cut off from the great open sea by the elevation of portions of the bottom upon which the Fox Hills deposits were made.”*

Wherever the Wahsatch Group was seen in superposition with the Laramie Group in our district, it was markedly unconformable, and also represented only the upper portion of the group. The regions in which it occurred were near the shore-lines of the Wahsatch Lake, and its conglomerates were seen resting unconformably on Silurian, Carboniferous, Jura-Trias, and Cretaceous strata, as well as on Post-Cretaceous. A considerable portion of the area that was below the level of the Laramie Sea became land probably before the end of the period, as the condition of the strata extending from Silurian to the Post-Cretaceous, inclusive, shows that a vast period of erosion intervened between the uplift and the time when the Wahsatch Group, or rather its upper portion, was deposited on the eroded edges of the older beds. This might perhaps be explained by the fact that a subsidence occurred which allowed the Wahsatch Lake to spread gradually over the regions where now we find only the upper beds of the group. This erosion, however, was on an enormous scale, and the whole of it could scarcely have been effected during the early Wahsatch time. Again: the fossils from the group in our district are all equivalent to those of the Bear River Estuary Beds, which Dr. White is inclined to think are older than the fossils from the group at other localities. He therefore thinks the upward movement of the Post-Cretaceous may have begun before the complete deposition of the strata composing the group.

This fact as to the age of the fossils taken in connection with the stratigraphical facts just noted render it very probable that the beds of the group exposed in Western Wyoming and Southeastern Idaho represent only the lower portions of the Laramie Group.

* Bulletin of U. S. Geol. and Geograph. Surv. of the Terr., vol. iv, No. 4, p. 866.

In the more central and eastern localities of the group, the overlying Tertiaries are conformable to the Post-Cretaceous, and the whole of the latter may probably be present, although even there there have been unconformities noted in the strata of the Laramie itself by Dr. White and others, so that, as Bannister remarks in the American Journal of Science and Arts for March, 1879 (p. 245): “The evidence" "indicates that the Laramie epoch was throughout one of stratigraphic disturb ance rather than that there was only one great orographic change at its close."

In Western Wyoming and adjacent regions there was intense orographical disturbance after the deposition of the beds that there represent the group. Then also occurred the folding that resulted in the formation of Meridian fold and the Wyoming and Salt River ranges, which was accompanied by the faulting seen along the eastern sides of the two ranges. The region westward from what is now the Green River Basin was lifted above the level of the sea and added to the land area which was farther west, and had been defined at the end of the Carboniferous. This uplift included the Wahsatch region of our district that lies north of latitude 41° 45'. In this region there are a number of isolated monoclinal ranges, which are the eroded remnants of anticlinal folds. The faults that are found farther south in the areas explored by the Fortieth Parallel Survey have in this region become ordinary folds. Speaking of these monoclinal ridges, King says: "The frequency of these monoclinal detached blocks gives abundant warrant for the assertions of Powell and Gilbert that the region is one prominently characterized by vertical action; yet when we come to examine with greater detail the structure of the individual mountain ranges, it is seen that this vertical dislocation took place after the whole area was compressed into a great region of anticlinals with intermediate synclinals. In other words, it was a region of enormous and complicated folds, riven in later time by a vast series of vertical displacements, which have partly cleft the anticlinals down through their geological axes, and partly cut the old folds diagonally or perpendicularly to their axes."

In regard to the monoclinal ridges within the limits of the district examined by me, the evidence is not difficult to obtain that they are simply the eroded fragments of anticlinals. The erosion forming them took place in the period which began with the Post-Cretaceous uplift, and has continued ever since. The faulting in the Wyoming and Salt River Ranges, as I have already stated, was probably synchronous with folding that occurred there.

Everywhere in the district there is perfect conformability from the Cambrian to the top of the Laramie as it is exposed in the district. This Laramie, as already stated, probably only represents the older portions of the group. Its fossil remains appear to indicate this. The fossils of the more eastern Laramie Group are not found in it, nor have the * Report Geol. Expl. Fortieth Parallel, vol. i, Systematic Geology, p. 735.

fossils of the former been found in the latter, and yet both have been considered conformable to the Fox Hills Cretaceous. If they represent different portions of the group, localities may yet be discovered in which the two will be in superposition. This, of course, is for the present a mere speculation, yet it seems to me that the facts point to the indication that these two localities represent two portions of the group separated by a period of orographic disturbance.

CONCLUSION.

In conclusion, I briefly recapitulate the points indicated by the facts observed in Western Wyoming and Southeastern Idaho.

1. During the period represented by the deposition of the Laramie Group as observed in the district, there was a progressive subsidence followed at the close by a general elevation, which perhaps foreshadowed the disturbance which was to take place after the complete deposition of the beds.

2. The fossils of the group thus described are equivalent to those of the Bear River Estuary Beds, which Dr. White is inclined to think are older in their facies than those of more eastern localities.

3. Intense orographical disturbance took place at the end of the deposition of the beds comprising the group in these localities, which resulted in the upheaval of the area west of Green River Basin to beyond the limits of our district, accompanied by great folding and faulting in the strata of the district.

4. It is probable that this disturbance took place before the close of the Post-Cretaceous period, and resulted in the separation of the Laramie Group into at least two portions, an eastern and a western part.

5. There was a period of vast erosion which began in the time immediately following the uplift, and has continued to the present time.

6. Following the disturbance, there was a progressive subsidence by which the western limits of the eastern or newer Laramie beds were overlapped, and which continued until the Upper Wahsatch fresh-water beds were deposited unconformably on the upturned and denuded edges of Silurian, Carboniferous, Jura-Trias, and Cretaceous, as well as the older Laramie strata.

Art. XIII.—On Lithophane and New Noctuidæ.

By A. R. Grote.

Prof. Fernald, on his recent journey to Europe, kindly took with him a series of our Lithophanes to compare with Mr. Walker's types in the British Museum. He took with him in particular specimens of the series of forms which cluster around L. cinerea (Riley), and which we have separated in the collection under different names. These are L. cinerea, laticinerea, unimoda, and cinerosa n. s. This latter is darker than any of the others, with the paler shadings of very light gray contrasting. It is large, very hairy, and with the orbicular very bright and light gray. This form is taken commonly by the Albany collectors, who regard it as distinct. It has been in MSS. in my collection for a long time, but I have hitherto hesitated to separate it from laticinerea. Prof. Fernald writes me the result of his examination, as follows:

"The only Xylina which I found in the Walkerean collection, under a different name from what they are known by us, was Xylina antennata Walk. (habitat unknown). This is = X. cinerea Riley. There can be no mistake on this, for Mr. Butler and my wife both compared them, and we all agree, without the shadow of a doubt."

In my own visit to the British Museum in 1867 I had no North American Xylinas with me to compare, but I noted that antennata was a gray species, which I thought I had seen in our collections; but on my return home I could not remember with sufficient accuracy which of the gray forms Mr. Walker had. Prof. Fernald writes further respecting Mr.

Walker's other species unidentified by us:

“X. infructuosa Walk. is in too poor condition to be certain of; it is near, if not identical with, X. petulca. X. spoliata is new to me; I doubt its generic location; the eyes are hairy. X. commoda is a very dark species, without markings; I doubt if it is a Xylina. X. claufacta Walk., too poor to determine; not a Xylina; hind wings very light or white, save border and costa."

Prof. Fernald has by these observations made it tolerably safe to describe our species, and has settled the synonymy in important points. L. cinerea is the only one of the gray forms of our Lithophanes which shows any decided ferruginous or brown shades about the reniform spot or s.t. line and basal dash, as described by Walker, whose description, nevertheless, is far from satisfactory. It is the smallest in average expanse of the gray forms. I refer the student to my Check List, Part II, for the synonymy of this generic term, which should be used in preference to Xylina.

Bull. V, 2-4

201