The second volume of Lyell's work is the most widely read because of its influence on Charles Darwin. Darwin received a copy during his voyage on the Beagle and read it as he was making his observations, collecting samples, etc. Lyell undoubtedly contributed an emphasis on actualism and gradualism as well as a lot of information on species and their relation to their environments. The result of this influence is that this volume is often read to assist an understanding of Darwin's ideas - thus Secord's edition samples this volume rather fully compared to the others and selects some chapters that are particularly relevent to Darwin's ideas.
The stress on Volume II is, in some ways, unfortunate because Lyell's third volume actually reveals his interpretation of Earth history most clearly. However this does allow us to see how Lyell carries his interpretive framework into the organic world. It is not too difficult to see how Darwin would make use of much of the information gathered by Lyell (and other naturalists) in developing his theory.
Rudwick's summary outlines the main points including Lyell's key conclusions that (1) species are stable and unvarying entities that are suited for their physical environment, (2) species have been in a rather uniform flux through time, and (3) this flux was driven by gradual and continuous changes in the physical world (as had been documented in Volume I). The full significance of these conclusions will be clear when we turn to Volume III.
I will ask you to work in small groups during our examination of Volume II, and to collectively write up an outline of the contents.
Chapters 1-4 (p. 183-233)
Lyell opens Volume II with a discussion of species spread out over the first four chapters. Chapter 1 includes some general introductory comments (opening paragraphs) and then moves into a summary of Lamark's theory. The basic question is whether species change into another ("transmutation"). You may have encountered Lamark's ideas under the term "aquired characteristics" - the idea being that the activities of an organism during its life lead to tiny changes that are adaptive and inheritable. The broader picture is of a mosaic of "progressive development" in the organic world. Lyell outlines some of the various attributes and implications of Lamark's ideas.
Chapters 2-4 present Lyell's counter-arguments to species transmutation. As Rudwick comments, Lyell follows in the steps of Cuvier who had earlier argued against transmutation in debates with other French naturalists, and for the reality of individual species.
The bulk of chapter 3 develops an argument for the reality of variability within a species, and chapter 3 deals with the limits on the variabiltiy. Together these are essentially an attack on the basic premise of species transmutation that species can change by an accumulation of ongoing variations into other species. The discussion of species variability in chapter 2 draws heavily upon human experience with domesticated plants and animals. This approach follows Lyell's earlier comments about using well-known organisms as models. You should consider his arguments that some species will necessarily have more variability, and that humans domesticated those plants and animals with the most variability (p. 200-202). Chapter 3 continues the variability discussion by shifting the focus onto the limits of variation, with the idea that variability cannot be extrapolated to the point of transmuting one species into another.
You may be struck by the rather free use of the notiion of "creation" and attribution of species characteristics to the "Author of Nature". This was typical of Lyell and his contemporaries, and does not indicate a belief in direct divine creation of new species. The origins of species was one of the great unknowns of the natural world prior to Darwin's work. Naturalists accepted the idea that new species appeared at some point through some unknown natural causal mechanism. They recognized that species were suited to the particular environment/habitat in which they appeared. (If you want to know more about this perspective, consult M. J. S. Rudwick, 1976, The Meaning of Fossils, second edition.)
Chapter 4 turns to the problem of hybrids. I want to make a some brief comments on hybrids that may help you understand Lyell's points: My impression from the biological literature is that hybrids are much more common among plants than animals. Very few animals successfuly reproduce across species barriers, and the offspring are almost always sterile. Closely related plants are more likely to produce hybrids because some of the natural barriers to reproduction are related to habitat, flowering times, etc. - barriers that are less effective for most animal species. Hybrids may form if humans manipulate the natural system to overcome these barriers. However such hybrids are still infrequent.
The chapter closes (p. 232-233) with a list of six major points that summarize the first four chapters. The first five are explicitly discussed, but the last is more of an inference (albeit a common one at the time).
To do...
You should try to outline Lyell's basic arguments about species. I would suggest that you start with the basic points at the end of chapter 4 and try to outline the evidence for them.
A secondary issue is what is the significance of all this. Why does it matter that species are stable entities that vary within certain limits? How might you expect Lyell to make use of this conclusion? Can you link it back to his perspective on the physical world (Volume I) - in particular, to his ideas on the relationship between climate and the fossil record?