132 



SCIENCE. 



[Vol. XXI. No 527 



SCIENCE: 



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AN OLD VOLCANIC ERUPTION IN IOWA. 



BY CHARLES R. KETES, DBS MOINES, IOWA. 



In the extreme northwestern corner of Iowa there is a small 

 area of crystalline rocks commonly known under the name of the 

 Sioux Quartzite or Sioux "Granite." These are the only strata 

 in the State showing any decided traces of being changed through 

 dynamic influences. Everywhere else within the limits of the 

 province the rocks are so horizontal in tlieir position, so undis- 

 turbed by mountain- making forces, and so unaltered in lithologi- 

 cal characters, that it is generally taken for granted that all the 

 strata in the State are sedimentary in origin and repose essen- 

 tially as they were originally laid down in the waters of the 

 great interior sea which once occupied the heart of the American 

 continent. 



The Sioux quarzite is a hard, vitreous mass with undulating 

 bedding planes. Its geological age is regarded as much greater 

 than that of any other formation in Iowa; not excepting even 

 the old Cambrian sandstone of the northeastern portion of the 

 State. 



Although the area of the Sioux quartzite is quite extensive, no 

 other crystalline rocks have been noted in the neighborhood until 

 very recently. It is, then, of considerable interest to know that 

 Professor G. E. Culver has lately discovered in the midst of the 

 Sioux quartzite, of southeastern Dakota, in Minnehaha County, 

 within three miles of the Iowa boundary, a large mass of trap, 

 which extends for more than a mile along one of the tributaries 

 of the Big Sioux River. A microscopical examination of these 

 rocks shows it to be a well-pronounced, coarse-grained, olivine 

 diabase, with such minerals as hornblende, black mica, and apatite 

 present in addition to the feldspar, augite, and olivine. 



The presence of this massive basic rock of unmistakable erup- 

 tive origin is very suggestive of the agencies that have been at 

 work to some extent in changing the old sandstone. Further 

 investigations will doubtless disclose othfr similar types of in- 

 trusive rocks in the Sioux quartzite in all three of the States 

 already mentioned. 



But the occurrence of this black trap rock, which has un- 

 doubtedly been cooled from a molten condition, is made even 

 more interesting by other discoveries of still more recent date. 

 During the past few years a number of deep wells or borings 

 have been made at different places in northwestern Iowa. The 

 depths reached are from 1200 to 2000 feet. Several of these bor- 

 ings are of special interest, inasmuch as thej' pass through all of 

 the sedimentary rocks into the crystalline beds below, penetrating 

 them in some cases to the extent of several hundred feet. A 

 typical gray granite has been recognized in some instances; in 

 others different types of eruptive rocks. One of the latest borings 

 in this part of the State is the well at Hull, in Sioux County. At 

 a very considerable depth a number of beds of flint-like rock were 

 passed through. The different layers were separated by sand and 

 gravel several feet in thickness, if the records are to be relied 

 upon. Some of the flint-like fragments were sliced by Mr. S. W. 



Beyer of the Iowa Agricultural College, and upon microscopical 

 examination proved to be what is known to geologists as quartz- 

 porphyry — a truly igneous rock or lava, very acid in character, 

 and essentially identical with granite, but cooling under some- 

 what different physical conditions. 



The presence of the several sheets of quartz-porphyry, which 

 are to be regarded as different lava flows, show conclusively that 

 volcanic forces were very active in northwestern Iowa in ancient 

 times. The position of the lava beds seems to indicate, as will be 

 pointed out by Mr. Beyer in his discussion of the subject in the 

 forthcoming Annual Report of the Iowa Geological Survey, that 

 the flow of the molten rocks probably took place toward the close 

 of the Carboniferous age, immediately after the coal of the Mis- 

 sissippi basin had been deposited. 



Mr. Beyer puts forward, therefore, two explanations: — 



1. That the flow took pl^ce during palseozoic time, perhaps in 

 the Carboniferous, the lava being secularly poured out over an old 

 sea-bottom. 



2. That, as a whole, the different flows were contemporaneous 

 and in point of time post- Carboniferous. In this case the inter- 

 calations are to be regarded as the results of the subterranean 

 lava flows — the lava following along lines of least resistance and 

 flowing between the strata. 



It makes little difference which of these two views is accepted, 

 for certain it is that here in northwestern Iowa there is everj' 

 reason for believing that there were at one time active volcanie 

 agencies at work not unlike those seen to-day in southern Europe, 

 around the shores of the Mediterranean Sea. 



THE PERMIAN IN PRINCE EDWARD ISLAND. 



BT F. BAIN, NORTH RIVER, P. E. ISLAND. 



The study of the Permian in North America hitherto has not 

 been satisfactory. The area« studied west of the Mississippi and 

 in Virginia exhibit the lower part of the formation which in 

 organic remains so closely resembles the Upper Carboniferous 

 that a clear and satisfactory periodic distinction is not observa- 

 ble. In the Gulf of St. Lawrence, however, where a long-con- 

 tinued and regular subsidence marked the close of the palaeozoic, 

 we have a perfect series of the Permian strata, three thousand 

 feet in depth, recording the gradations of life in this district 

 between the close of the Carboniferous proper and the beginning 

 of the Mesozoic. 



The Island of Prince Edward, in the southern part of the Gulf 

 of St. Lawrence, is composed of red sandstones and shales, mostly 

 Permian, capped in the central district by a denuded fragment of 

 the Trias. Where these Permian beds stretch across the Northum- 

 berland Strait and appear on the coast of New Brunswick, they 

 are seen to repose unconformably on the Carboniferous. Here 

 the distinction between the two formations is very apparent The 

 Carboniferous is a coarse, gray marsh deposit, bearing numerous 

 remains of Calamites and Cordaites and a few Lepidodendra. The 

 Permian consists of fine, red marine deposits, bearing as their 

 characteristic organisms Walchia, Tylodendra, Baiera, Pecop- 

 teris arborascens, and Calamites gigas. 



In the lower part of the Permian the flora has marked Carbon- 

 iferous affinities, but there is always a clear and distinct differ- 

 ence. On St. Peter's Island, for example, theie is a marsh de- 

 posit of the Permian. The gray and brown sandstones and gray 

 bleached clays contain but few calamites, and these of small size, 

 except the giant C. gigas. Cordaitesis also inconspicuous, but re- 

 mains of Tylodendra and Walchia are in great, profusion, and- 

 Annularia frequent. At Gallas Point there is the same abundance 

 of Tylodendra and Walchia with Dadoxylon and Pecopteris, and 

 here, as in the other localities, C. arenasceus begins to take pre- 

 cedence of the older Carboniferous calamites. At Mimimigash 

 is an extensive fern deposit in red clay shale. Pecopteris arboras- 

 cens is abundant and is in magnificent development. Its great, 

 heavy fronds are seen nine feet in length, and its features rich 

 and well developed. Alethopteris nervosa is common, but Sphe- 

 nopteris, Neuropteris, and Cyclopteris are sparsely represented. 

 Annidaria is abundant. Cordaites and Calamites hold a minor 



