110 ANNALS NEW YORK ACADEMY OF SCIENCES 



west belt, from the head of Bush Eiver, in Hartford County, to Wash- 

 ington, D. C. 



.. The Arundel consists typically of drab, more or less lignitic clays, with 

 masses of siderite. The nodules and geodes of siderite, when exposed to 

 the air, often change to brown hematite. The clays are usually free from 

 grit, but are occasionally sandy, and in places carry pyrite and gypsum. 

 Lignite beds also occur. 



^ - The thickness of the formation is not great, the maximum being about 

 125 feet, and usually it is much less than that. It is thickest on the 

 western side or middle of the belt, and thins eastward as shown by borings. 

 The Arundel overlies the Patuxent disconformably, and appears to 

 occupy old drainage lines in the Patuxent. Cross-bedding is occasionally 

 found in the lower beds, but is not usually present. The formation is 

 overlain, with disconformity, by the Patapsco formation. The fauna will 

 be discussed in the section on the age of the Morrison formation. 



SUMMAKY OF StRATIGRAPHIC EeLATIONS AND CpTARACTERS OF THE 



Morrison Formation 



The stratigraphic relations and characters of the Morrison are sum- 

 marized in the following pages. 



DISTRIBUTION 



The Morrison formation has a wide distribution in Utah, New Mexico, 

 Colorado, Wyoming, Montana, South Dakota and perhaps Idaho and 

 Arizona. The number of square miles of Morrison outcrops is not very 

 great, but the area in which the Morrison is overlain by younger deposits 

 probably includes several hundred thousand square miles. The areas 

 from which the Morrison has been eroded probably includes mauy thou- 

 sand square miles more. 



The formation, after deposition and before burial or erosion, had an 

 extremely wide distribution, which may have amounted to four or five 

 hundred thousand square miles. 



RELATION TO UNDERLYING ROCKS 



In various areas the Morrison rests on formations of different ages, 

 ranging from Archean to upper Jurassic. In the southwestern areas the 

 Morrison or McElmo rests on the La Plata sandstone of Jurassic age. 

 The contact with the La Plata is apparently conformable, but there is a 

 decided break beneath the La Plata. The latter lies on the Dolores beds 

 of Triassic age, in some localities; on the Cutler, Hermosa and Elbert 



