The "train of disaster" metaphor is Carson's way of describing the lasting effects of pesticides on the natural environment. She establishes the metaphor in the opening of her essay. Carson suggests that the process of spraying to kill insects is a result of the immense power for altering the environment that human beings possess: "Only within the moment of time represented by the present century has one species—man—acquired significant power to alter the nature of his world." This reality has established a "process of spraying" which has established an "endless spiral." Carson sees the problem which has resulted from this as having brought about a "train of disaster in its wake." This is what Carson views as the "accomplishment of our modern way of life." The train of disaster is Carson's way to express the destructive nature of human use of pesticides. Carson makes the argument that there is an ecosystem balance of which humans are a part.
In using pesticides, humans have created irreparable damage to themselves and the other creatures that inhabit the planet. Carson's point in using the metaphor is to show how the interconnected nature of living organisms means that everyone and everything is impacted through the use of pesticides. Carson's point in using the metaphor is to express the connectivity of life that has been disrupted through the use of pesticides. In doing so, the "train of disaster" becomes a haunting reminder that what human beings do today will have inescapable consequences tomorrow. This train continues on and stops for no one.
Thank you so much. Now I totally understand. (: you've been a HUGE help.