458 Bibliographical Notices. 



Of the latter the Potomac group is the chief mass, consisting of six 

 or seven formations. Its lower portion is decidedly of marine 

 origin and of Cretaceous age, extending northward to New Jersey. 

 Overlying these are some Eocene formations (Nanjemoy and 

 Aquia). They are succeeded on the south-east by the Miocene 

 deposits, formerly known as the Chesapeake group, but now divided 

 by the State Geological Survey into three well-defined formations — 

 " the Calvert, Chaplank, and St. Mary's," 



The Chesapeake group consists of variously coloured clays and 

 sands, sometimes fully charged with shells ; especially when 

 comminuted ; these form limestone ledges. The low^er part of the 

 Calvert series is rich in Diatomaceous beds, in places 20-40 feet 

 thick. 



Gravel, sand, and clay, probably of Pliocene age, are noticed in 

 Maryland. Later deposits of the mid-Atlantic slope, known as the 

 Columbia group, of Pleistocene age, have been divided by the 

 Geological Survey into three divisions ; the oldest of these, namely 

 the Sunderland, consists of gravel, clay, and loam, with ice-borne 

 boulders on the highest lands on the west shore of Chesapeake Bay. 

 The Wicomico in formation is similar to the Sunderland and skirts 

 the high-land capped by the former. The Talbot, somewhat similar 

 in formation, occupies the low level of the Coastal plain, seldom 

 rising above 40 feet. It has much peat and boulders and larger 

 areal extent than other Pleistocenes. 



The continuous examination of the fine series of fossiliferous 

 strata has been well carried out, and its various characters have 

 been studied both individually and in relation with similar geolo- 

 gical formations in other parts of the world. 



The different areas of local seas during the great period defined 

 as the Miocene or Mid-Tertiary, their shifting coasts, varied sea- 

 bottoms and faunal characters, and their successive climatic changes 

 can be fairly well indicated by geologists careful in work and in 

 arriving at philosophical conclusions. This aspect of the subject 

 is elaborated by W. H. Dall and others at pages cxxxiv-clv, on the 

 basis of the comprehensive tabular lists of the Maryland species, 

 according to local distribution, at pages xciv-cxxi, and of the 

 Mollusca alone in their general geographical and geological distri- 

 bution (pages cxxiv-cxxxvii). 



The systematic palfeontology of the Miocene formation of 

 Maryland is very fully described and illustrated in Part II., pages 

 1-508, with 132 plates and some figures in the text. Scrupulous 

 exactitude appears to have been the rule in both descriptions and 

 drawings, and so abundant and so excellent are the figures that 

 they may serve the student with materials sufficient (with some 

 groups of fossils) to make him w^ell acquainted with the facies of 

 generic and even specific groups. For fossil Yertebrata (Mammalia, 

 Aves, Reptilia, and Pisces) see plates 10-32 ; Cirripedia, pis. 33, 

 31 ; Ostracoda, pis. 35-38 ; one Cephalopod and many Gasteropods, 

 pis. 39-63 ; Amphineura and Scaphopoda, 1 plate ; Pelecypoda, 

 pis. 65-108 ; one Brachiopod and many Bryozoa and one Spirorbis, 



