AucrsT ;ii, I8s.'j.] 



SCIENCE 



•i(ii) 



engineering ; and that part of the science which 

 lins iiitherto been in a most unsatislaclorv con- 

 flition, as viewed from the standpoint of tlie 

 engiiieer engaged in its api)licalion, may bo 

 found to taiie a comparatively complete and 

 useful foi'm." 



GEOLOGY OF PIIILADELPIHA. 



The qeolofjij nf Phi/nil el /)fiia : a lecture itelirereil be- 

 f'lre lite Fniiikiin iii.-tioile, Jan. 12, 1SS3. By 

 Professor Henry Cauvill Lkwis. riiiladel- 

 phia, 1833. 21 p. 8°. 



TnK author has distributed Ids pamphlet 

 edition of this important paper, whicii deserves 

 extended notice, and has placed him in the 

 front rank of the young prosecutors of original 

 research in the field of geology in this country. 

 This memoir, and his previous lecture on the 

 Ice age in I'einisylvania. have the rare merits 

 that they are solid contributions to our knowl- 

 edge from the first to the last pages ; that 

 they are almost exclusively due to the personal 

 labors of the young geologist who brings them 

 in their very com|)lete form before tiie world ; 

 tliat they are closely and fairly reasoned out, 

 and lucidly expressed. The great societies of 

 the learned whicli reijiiire for membership the 

 l)roduction of a work showing important, new, 

 and original researches, have accepted many 

 essays inferior in all these particulars to the 

 subject of this review. To fully api)reciate its 

 merit, one must consider how very vague were 

 the notions of geologists (including tiie large 

 and growing class of Flnladel|)hia geologists) 

 as to our superlicial deposits, before its ai)pear- 

 ance. The great intluence of Louis Agassiz, 

 and his theories of universal glaciation, had 

 restricted the number of those who sought to 

 deliue the action of glaciers in our continental 

 geology, by extending the limits of this action 

 over I he tropics. The explanation of any thing 

 obscure by the words 'glacial action ' became 

 almost as common as the explanation of any 

 thing dilHcult in physiology used to be b}' the 

 words ' lusus naturae.' 



It required, therefore, peculiar independence 

 of thought to break loose from these Active 

 (always the most insurmountable) fetters, and 

 to see the plieuomena with^one's own eyes. 

 Besides this, it required laliorious journeys, 

 patient note-taking, and attentive reading of 

 what others had done, in order to do justice to 

 the suliject, and prepare a monograph upon it. 

 -\11 these Professor Lewis has accomplished; 

 ancl. though much remains to be done, few 

 iiresented so com|)lete and neat a view of 

 subject as he has. 



It will alreatly appear to be the writer's 

 view, -that his matter, and his manner of pre- 

 senting it, have been found admiral)le, though 

 as to the latter, his system, while sui)ported 

 by a clear style, will necessarily present some 

 ditlicidties to tlie superficial reailer. He could 

 either have begun from the exterior and older 

 boundaries of his superficial formations, and 

 have proceeded inwards towards the present 

 river Delaware ; or he could have adopted his 

 present plan of commencing in the middle 

 with the red gravel, — inverting somewhat the 

 order of the overlying sediments by consider- 

 ing the alluvium next (which is at the top of 

 all), taking next the Trenton gravel (which 

 underlies the latter), and completing the upper 

 part of the column by treating of the Phila- 

 delphia brick clay (which belongs between the 

 upland terrace material, first mentioned, and 

 the Trenton gravel), — and then following the 

 column downward through the red, yellow, and 

 Hryn-JIawr gravels, finishing by a short sketch 

 of the underlying rock formations ; or he might 

 have proceedeil geographical I}' from the newer 

 deposits on the river, outwards to the Bryn- 

 Mawr terrace. 



The writer confesses, that, in view of the per- 

 fectly consistent theory which Professor Lewis 

 has evolved, it would seem easier to follow the 

 chronological order of the events which this 

 theory comprehends, even though the geo- 

 graphical sequence were somewhat disturbed ; 

 but this criticism does not alfect the real value 

 of his results. 



Those who read this essaj* as carefully as it 

 deserves will be rewarded by obtaining a very 

 probable history of this portion of our conti- 

 nent during post-tertiary time, with its submer- 

 gences and elevations and the consequences 

 thereof. It is perhaps to be regretted that 

 Professor Lewis has not treated with the same 

 care the subordinate part of his subject, to 

 which he devotes a few concluding words ; 

 that is to say, the 'gneiss,' the "auroral lime- 

 stone,' and the ' triassic san<Istone.' Thus, he 

 confounds the views of two masters of our 

 American geology in ascribing the gneiss of 

 Philadelphia in the same breath to the Iluroni- 

 an and the Jlont Alban.' 



It is also somewhat v.aguc to s.ay ' the gneiss 

 of the Rocky Mountains of Colorado ; ' since 

 there are different gneisses belonging to differ- 

 ent ages there, some of them probably Mont 

 .VIban, some Iluronian, and some very likely 

 Laurentian. 



Again : it is conceded by most Philadelphia 



' Compare Pr. T. .Sicrry IliiiitV 

 in., vol. E. p. aoo. 



2J i;.(.l. 



