l6l MURFREESBORO STAGE — OLSSON 



outside Miocene. This relation is illustrated beautifully amongst 

 the gastropods where the whole aspect of several families of 

 shells is markedly different between the two states. For example in 

 the family Tirritidce {Pleurotomidce) , the prevalent generic types 

 in Maryland are Turris and Surcula, while that of the Drillia- 

 like forms are much less in evidence. In the Murfreesboro and 

 the Yorktown, not a single species of the genera Turris and Sur- 

 cula are known, while Drillia is very abundant both in species 

 and individuals. The smaller Nassas of the upper Miocene have 

 a distinctly modern appearance, very different from the IyOwer 

 and Middle Miocene species. Another example might be 

 selected from the Terebridcs. In the Maryland Miocene this 

 family is well represented by the genus Hastula and compara- 

 tively few true Terebras. The genus Hastula is entirely unknown 

 in the Virginia and Carolinian Miocene. Its place is taken by 

 a multitude of true Terebras, many of which are related to recent 

 types. Further examples are unnecessary, but a number of 

 others could be selected and would furnish much the same sort 

 of evidence. 



The highest stratigraphic stage of the Maryland Miocene is 

 the St. Mary's and therefore approaches most nearly the age of 

 Murfreesboro. Its fauna is peculiar, easify identified and of 

 rather limited distribution. It is well developed at its type ex- 

 posures along the St. Mary's river, at Cove Point, and I,angley's 

 Bluff, Md. In New Jersey, the stage has been recognized in 

 several deep wells, as at Atlantic City, Wildwood, etc. In north- 

 ern Virginia, beds of the same age occur along some of the north- 

 ern rivers as on the Rapphannock. 



In Maryland, where the St. Mary's stage is best known, it 

 is characterized essentially by a gastropod fauna. At its type 

 exposure, the following forms are very abundant: Actceon ovoides, 

 Hastula simplex, Turris communis, Raphitoma parva, Crassispira 

 incilifera, Busy con coronatum, fusiforme, Buccinofusus parilis, 

 Nassa peralta, Turritella plebeia, Calliostoma humile. Amongst 

 the pelecypods, the more conspicuous are Spisula subponderosa and 



