52 Prof. Dr. Pavloic — Oligocene Sandstone in Neocomian Clays. 



W. Cross describes (Bull. Geol. Soc. of America, vol. v, p. 22;')) 

 intrusive sandstone dikes in granite occurring in the Pikes Peak 

 region in Colorado ; no fossils were found in the sandstone, the 

 source of sand and the time of its intrusion not being defined. 

 Mr. J. S. Diller refers, in Bull. Geol. Soc. of America, vol. i, p. 439, 

 to many other cases of sandstone dikes discovered in many countries 

 (by Ch. Darwin in California, by J. D. Dana in Oregon, by T. D. 

 Whitney in California, by W. J. McGee in eastern-central Mississipi). 



The features which distinguish the Neptunic dike of Alatyr from 

 the above-mentioned are that the rock in which it is enclosed is soft, 

 while the rock forming the dike itself is in some places a hard 

 sandstone, and in others a friable sand. 



Our Alatyr dike more closely resembles the sandstone dikes cutting 

 Cretaceous shales in the noi'th-western border of the Sacramento 

 valley in California, carefully described by Mr. J. S. Diller. 1 These 

 sandstone dikes, which are exposed in the valleys of several streams 

 tributary to Cottonwood creek, strike to the north-east, are more or 

 less parallel one to another, and in cutting the shales are inclined 

 15° to the north-east. The thickness of these dikes varies from two 

 to fourteen or twenty inches, and the largest dike is fifteen feet thick. 

 The sandstone forming the dikes is more or less homogeneous, and 

 frequently includes small fragments of shale along their borders. 

 The shales which contain the sandstone dikes are covered by the 

 newer formations of the Sacramento valley. In explaining the 

 origin of these dikes Mr. Diller calls attention to certain phenomena 

 frequently associated with earthquake movements. Thus, during 

 the great Calabrian earthquake of 1783 many fissures were formed 

 in the ground, and from some of them great quantities of sand and 

 water issued. After the flow ceased, the openings wei'e left full of 

 sand. Similar phenomena accompanied the earthquakes of New 

 Madrid, Missouri in 1811-1813, of Valparaiso in 1822, of Sonora in 

 1887, etc. 



The formation of a system of parallel fissures by earthquakes, and 

 their being filled with sand forced up from below is, according to 

 Mr. Diller's view, a phenomenon identical with the formation of the 

 sandstone dikes of Sacramento region, these dikes thus being a record 

 of ancient earthquake movement. A sandy bed of the same Cretaceous 

 seiies, cropping out from under the shales which are cut by the 

 dikes, about seven miles westwai'd of the principal group of dikes, 

 is considered to be the source of the sand in the dikes. Thus, 

 according to Mr. Diller's view, the sand is carried up by an ascending 

 current of water from a lower, i.e. from a more ancient bed. In the 

 absence of fossils it was scarcely possible to prove this positively. 



Is such an explanation applicable to our case ? We must reply 

 in the negative. Our case makes it possible to give a somewhat 

 different explanation. Our conditions are more favourable, fossils 

 being preserved in the rock forming the Neptunic dike of Alatyr. 

 It can positively be decided whether the sandstone of the dike is 



1 Bull, of the Geol. Soc. of America, 1S89, vol. i, pp. 411-442. 





